Science Practice Paper 2019-20 Questions And Answer HELP

Welcome to the Science Practice Paper 2019-20 Questions and Answer for the Central Board of Secondary Education (CBSE) Class 10 examination. This resource is designed to help students prepare for their exams by providing detailed solutions and explanations to a set of practice questions.

By reviewing these answers and diagrams, students can gain a better understanding of key concepts, improve their problem-solving skills, and feel more confident for their upcoming science board exam. Best of luck with your preparation! 📝

Science Practice Paper 2019-20 Questions and Answer

1. Define catenation.

Catenation is the self-linking property of an element, particularly carbon, to form chains, rings, or other complex structures.

2. How does valency of an element vary across a period?

Valency is the combining capacity of an element. As you move across a period, the valency with respect to hydrogen increases from 1 to 4 and then decreases to 1. Valency with respect to oxygen increases from 1 to 7.

4(c) Which one of the following diets would you recommended to the affected patient? i) High sugar and low fat diet. ii) Low sugar and high protein diet. iii) High Fat and low fiber diet. iv) Low sugar and high fiber diet. The correct option is

iv) Low sugar and high fiber diet.

4(d) Refer to the Table A and suggest the value of the mean blood glucose level beyond which doctor’s advice is necessary: i) 180 mg/dL ii) 115 mg/dL iii) 50 mg/dL iv) 80 mg/dL The correct option is

i) 180 mg/dL.

5 When we enter a dark room coming from outside, immediately the things inside the room do not appear clear to our eyes. This is because i) pupils do not open at all in the dark. ii) pupils take time to adjust. iii) light travels slower in a dark room. iv) pupils open very quickly in the dark. The correct option is

ii) pupils take time to adjust.

The phenomena of light responsible for the working of the human eye is i) reflection ii) refraction iii) power of accommodation iv) persistence of vision The correct option is

ii) refraction.

6 When a 4V battery is connected across an unknown resistor there is a current of 100 mA in the circuit. The value of the resistance of the resister is: i) 4 Ω ii) 40 Ω iii) 400 Ω iv) 0.4 Ω The correct option is

ii) 40 Ω.

7 Unit of electric power may also be expressed as: i) volt-ampere ii) kilowatt-hour iii) watt-second iv) joule-second The correct option is

i) volt-ampere.

8 It was found that water from a river was contaminated with Coliform bacteria. Which one of the following pollutant might have got mixed with the water? i) Fertilizer run off ii) Industrial waste iii) Pesticides iv) Human faecal matter The correct option is

iv) Human faecal matter.

Which one of the following stakeholders of forests causes the maximum damage to forest? i) People who live in or around the forest ii) The forest department of the government iii) The wildlife and native enthusiasts iv) The industrialists The correct option is

iv) The industrialists.

9 Which one of the following green house gases is a contributor due to incomplete combustion of coal and petroleum? i) Oxides of nitrogen ii) Methane iii) Carbon monoxide iv) Carbon dioxide The correct option is

iii) Carbon monoxide.

10 Which of the following reactions is an endothermic reaction? i) Burning of coal. ii) Decomposition of vegetable matter into compost. iii) Process of respiration. iv) Decomposition of calcium carbonate to form quick lime and carbon dioxide. The correct option is

iv) Decomposition of calcium carbonate to form quick lime and carbon dioxide.

11 Identify the basic salt from the following salts: i) Na2CO3 ii) NH4Cl iii) NaNO3 iv) KCl The correct option is

i) Na2CO3.

12 The positions of four elements A, B, C and D in the modern periodic table are shown below. Which element is most likely to form an acidic oxide? i) A ii) B iii) C iv) D The correct option is

iii) C.

Elements P, Q, R and S have atomic numbers 11, 15, 17 and 18 respectively. Which of them are reactive non-metals? i) P and Q ii) P and R iii) Q and R iv) R and S The correct option is

iii) Q and R.

13 Assertion: Following are the structural isomers of butane. Reason: Structural isomers have the same molecular formula but they differ in their structures. i) Both A and R are true and R is correct explanation of the assertion. ii) Both A and R are true but R is not the correct explanation of the assertion. iii) A is true but R is false. iv) A is false but R is true. The correct option is

i) Both A and R are true and R is correct explanation of the assertion.

14 Assertion: A fuse wire is always connected in parallel with the mainline. Reason: If a current larger than the specified value flows through the circuit, fuse wire melts. i) Both A and R are true and R is correct explanation of the assertion. ii) Both A and R are true but R is not the correct explanation of the assertion. iii) A is true but R is false. iv) A is false but R is true. The correct option is

iv) A is false but R is true.

15 (i) Write two observations when lead nitrate is heated in a test tube. (ii) Name the type of reaction. (iii) Write a balanced chemical equation to represent the above reaction.

(i) When lead nitrate is heated, two observations are:

A yellow solid (lead oxide) is formed.
Brown fumes (nitrogen dioxide) are evolved. (ii) This type of reaction is a thermal decomposition reaction because a single compound breaks down into two or more simpler substances upon heating. (iii) The balanced chemical equation is: 2Pb(NO3)2(s)Heat2PbO(s)+4NO2(g)+O2(g)

16 A compound ‘X’ of sodium is used as an antacid and it decomposes on strong heating. (i) Name the compound ‘X’ and give its chemical formula. (ii) Write a balanced chemical equation to represent the decomposition of ‘X’. (iii) Give one use of compound ‘X’ besides an antacid.

(i) The compound ‘X’ is Sodium hydrogen carbonate (also known as sodium bicarbonate or baking soda). Its chemical formula is NaHCO3.

(ii) The balanced chemical equation for its decomposition on heating is:

2NaHCO3(s)HeatNa2CO3(s)+H2O(l)+CO2(g)

(iii) Besides being an antacid, Sodium hydrogen carbonate is also used as a constituent of baking powder.

You are provided with 90 mL of distilled water and 10 mL of concentrated sulphuric acid to prepare dilute sulphuric acid. (i) What is the correct way of preparing dilute sulphuric acid? Give reason. (ii) How will the concentration of H3O+ ions change on dilution?

(i) The correct way to prepare dilute sulphuric acid is to add the concentrated sulphuric acid slowly to the water with continuous stirring. The reason for this is that the dilution of concentrated sulphuric acid is a highly exothermic process, meaning it releases a large amount of heat. Adding acid to water ensures that the heat is dissipated safely, as the large volume of water can absorb the heat. Adding water to acid would cause the water to boil violently and splatter the concentrated acid, which is extremely dangerous.

(ii) On dilution, the concentration of H3O+ ions will decrease. The number of hydronium ions remains the same, but they are distributed in a larger volume of solvent, thus reducing their concentration.

17 Two elements X and Y have atomic numbers 12 and 16 respectively. To which period of the modern periodic table do these two elements belong? What type of bond will be formed between them and why? Also give the chemical formula of the compound formed.

Element X with atomic number 12 is Magnesium (Mg). Its electronic configuration is 2, 8, 2. It belongs to Period 3 of the modern periodic table. Element Y with atomic number 16 is Sulphur (S). Its electronic configuration is 2, 8, 6. It also belongs to Period 3 of the modern periodic table. An ionic bond will be formed between X and Y because X is a metal (Mg) and Y is a non-metal (S). X will donate its two valence electrons to Y, forming Mg2+ and S2− ions. The electrostatic attraction between these oppositely charged ions will form an ionic bond. The chemical formula of the compound formed is XY, which is MgS.

18 (i) Create a terrestrial food chain depicting four trophic levels. (ii) Why do we not find food chains of more than four trophic levels in nature?

(i) A terrestrial food chain with four trophic levels can be depicted as follows: Grass (Producer) → Grasshopper (Primary Consumer) → Frog (Secondary Consumer) → Snake (Tertiary Consumer)

(ii) Food chains of more than four trophic levels are not common in nature because of the loss of energy at each trophic level. Only about 10% of the energy is transferred from one trophic level to the next, while the remaining 90% is lost as heat to the environment or used for metabolic activities. By the time energy reaches the fourth trophic level, very little useful energy remains to sustain another level, making it energetically unviable.

How will you create an artificial aquatic ecosystem, which is self-sustainable?

To create a self-sustainable artificial aquatic ecosystem, you would need a balanced microcosm containing all the components of a natural ecosystem.

Producers: Introduce aquatic plants like Elodea or duckweed to produce oxygen and food through photosynthesis.
Consumers: Add a few small aquatic animals, such as fish or snails, that can feed on the producers and each other.
Decomposers: Include beneficial bacteria in the substrate or water to break down organic waste from the consumers and plants, recycling nutrients back into the system.
Energy Source: Provide a light source for the plants to perform photosynthesis.
Maintaining Balance: The system must be sealed to prevent matter from entering or leaving, but light must be able to pass through. The waste from the consumers provides nutrients for the plants, which in turn provide oxygen and food for the consumers, creating a closed-loop, self-sustaining system.

19 Explain the processes of aerobic respiration in the mitochondria of a cell and anaerobic respiration in yeast and muscle with the help of word equations.

Aerobic Respiration in Mitochondria: This process occurs in the presence of oxygen. Glucose is completely broken down into carbon dioxide, water, and a large amount of energy. It takes place in the mitochondria of cells.
- Word Equation: Glucose + Oxygen → Carbon dioxide + Water + Energy
Anaerobic Respiration in Yeast: This process occurs in the absence of oxygen and is also known as fermentation. Glucose is broken down into ethanol (alcohol), carbon dioxide, and a small amount of energy.
- Word Equation: Glucose → Ethanol + Carbon dioxide + Energy
Anaerobic Respiration in Muscle: This also occurs in the absence of oxygen, typically during intense physical activity when there is insufficient oxygen supply. Glucose is broken down into lactic acid and a small amount of energy.
- Word Equation: Glucose → Lactic acid + Energy

20 In a pea plant, the trait of flowers bearing purple colour (PP) is dominant over white colour (pp). Explain the inheritance pattern of F1 and F2 generations with the help of a cross following the rules of inheritance of traits. State the visible characters of F1 and F2 progenies. Parental Generation (P):

Parent 1: Purple flowers (PP)
Parent 2: White flowers (pp)
Gametes: P and p F1 Generation:
Cross: PP x pp
Resulting Genotype: All offspring are Pp
Visible Character (Phenotype): All plants have purple flowers, as the dominant P allele masks the recessive p allele. F2 Generation:
Cross: F1 x F1 (Pp x Pp)
Gametes: P, p and P, p
Resulting Genotypes:
- PP (25%)
- Pp (50%)
- pp (25%)
Visible Characters (Phenotypes):
- 3/4 (75%) of the plants have purple flowers (PP and Pp genotypes)
- 1/4 (25%) of the plants have white flowers (pp genotype)

Punnett Square for F2 Generation: | | P | p | | :— | :— | :— | | P | PP | Pp | | p | Pp | pp |

21 Explain giving reasons the bending of the shoot tip of a plant towards light source coming from one side of the plant.

The bending of the shoot tip towards a light source is a type of phototropism, specifically positive phototropism. This is caused by the plant hormone auxin, which is produced at the shoot tip.

When light is coming from one side, the auxin hormone migrates to the shaded side of the shoot. The higher concentration of auxin on the shaded side stimulates the cells there to grow and elongate faster than the cells on the lighted side. This unequal cell elongation causes the shoot to bend towards the light source.

22 It is desired to obtain an erect image of an object, using a concave mirror of focal length of 12 cm. (i) What should be the range of the object distance in the above case? (ii) Will the image be smaller or larger than the object? Draw a ray diagram to show the formation of the image in this case. (iii) Where will the image of this object be, if it is placed 24 cm in front of the mirror?

less than 12 cm.

(ii) In this case, the image will be

larger than the object and will be virtual and erect.

(iii) If the object is placed 24 cm in front of the mirror, the object is at the center of curvature (C), because the radius of curvature (R) is twice the focal length (

R=2f=2×12 cm=24 cm). Therefore, the image will also be formed at the

center of curvature (C), which is 24 cm in front of the mirror. The image will be real, inverted, and of the same size as the object.

23 Suppose your parents have constructed a two-room house and you want that in the living room there should be a provision of one electric bulb, one electric fan, a refrigerator, and a plug point for appliances of power up to 2 kilowatts. Draw a circuit diagram showing an electric fuse and earthing as safety devices.

The circuit diagram should show the following:

A main power supply coming into the house.
A fuse or circuit breaker connected in series with the live wire for safety.
An earthing connection for safety, which connects to the metal casing of the appliances like the refrigerator and the plug point.
The electric bulb, electric fan, refrigerator, and plug point connected in parallel to the main supply. This ensures that each appliance gets the full voltage and can be operated independently.

24 In the figure given below, a narrow beam of white light is shown to pass through a triangular glass prism. After passing through the prism, it produces a spectrum XY on the screen. (i) Name the phenomenon. (ii) State the colours seen at X and Y. (iii) Why do different colours of white light bend at different angles through a prism?

(i) The phenomenon is called dispersion of light.

(ii) The colour seen at X will be Violet and the colour seen at Y will be Red.

(iii) Different colours of white light bend at different angles because each colour has a different wavelength. The refractive index of the prism material is different for different wavelengths of light. Red light has the longest wavelength and is bent the least, while violet light has the shortest wavelength and is bent the most.

24 (i) What is the visible spectrum? (ii) Why is red used as the stopping light at traffic signals? (iii) Two triangular glass prisms are kept together connected through their rectangular side. A light beam is passed through one side of the combination. Will there be any dispersion? Justify your answer.

(i) The visible spectrum is the part of the electromagnetic spectrum that is visible to the human eye. It is composed of a continuous range of colours, from red to violet, that are produced when white light is dispersed by a prism.

(ii) Red light is used as a stopping light at traffic signals because it has the longest wavelength among the colours of the visible spectrum. Due to its long wavelength, it is scattered the least by atmospheric particles such as smoke and dust. This allows it to travel the farthest and be seen clearly even in adverse weather conditions like fog or rain.

(iii) No, there will be no dispersion. When the first prism disperses the light, the second prism, which is placed in the inverted position, will recombine the dispersed colours. The light beam emerging from the second prism will be white light, as the second prism negates the effect of the first.

25 Metal X is found in nature as its sulphide XS. It is used in the galvanisation of iron articles. Identify the metal X. How will you convert this sulphide ore into the metal? Explain with equations. The metal X is

Zinc (Zn). Zinc is used in galvanization to protect iron from rusting.

To convert the sulphide ore (zinc sulphide, ZnS) into metal, a two-step process is followed:

Roasting: The zinc sulphide ore is heated strongly in the presence of excess air. This process converts the sulphide ore into its oxide.
- Equation: 2ZnS(s)+3O2(g)Heat2ZnO(s)+2SO2(g)
Reduction: The zinc oxide is then reduced to metallic zinc by heating it with carbon (coke).
- Equation: ZnO(s)+C(s)HeatZn(s)+CO(g)

26 State the reason for the following: (i) Aluminium oxide is called an amphoteric oxide. (ii) An iron strip dipped in a blue copper sulphate solution turns the blue solution pale green. (iii) Hydrogen gas is not evolved when most metals react with nitric acid. (iv) Calcium does not occur in free state in nature. (v) Sodium or potassium metals are kept immersed under kerosene.

(i) Aluminium oxide is called an amphoteric oxide because it reacts with both acids and bases to form salt and water.

(ii) An iron strip turns the blue copper sulphate solution pale green because iron is more reactive than copper and displaces copper from its salt solution. The colour change is due to the formation of iron sulphate (FeSO4), which is pale green.

(iii) Hydrogen gas is not evolved when most metals react with nitric acid because nitric acid (HNO3) is a strong oxidising agent. It oxidises the hydrogen gas produced to water and is itself reduced to any of its oxides (like N2O, NO, or NO2).

(iv) Calcium does not occur in a free state in nature because it is a highly reactive metal. It readily reacts with oxygen, water, and other elements in the atmosphere to form stable compounds.

(v) Sodium or potassium metals are kept immersed under kerosene because they are

highly reactive and react vigorously with both oxygen and moisture in the air. Kerosene prevents their contact with air and water.

27 The formulae of four organic compounds are given below: A (C2H4), B (CH3COOH), C (C2H5OH), D (C2H6). (i) Which one of these compounds A, B, C or D is a saturated hydrocarbon? (ii) Identify the organic acid and give its structural formula. (iii) Which of the above compounds when heated at 443K in the presence of concentrated H2SO4 forms ethene as the major product? What is the role played by concentrated H2SO4 in this reaction? Also write the chemical equation involved. (iv) Give a chemical equation when B and C react with each other in presence of concentrated H2SO4. Name the major product formed and mention one of its important uses.

(i) The saturated hydrocarbon is D (C2H6). Saturated hydrocarbons have only single bonds between carbon atoms. A (C2H4) is an unsaturated hydrocarbon (alkene) with a double bond.

(ii) The organic acid is B (CH3COOH), which is ethanoic acid (or acetic acid).

Structural Formula: (iii) Compound C (C2H5OH) (ethanol) when heated at 443K with concentrated H2SO4 forms ethene (C2H4).
Role of Concentrated H2SO4: It acts as a dehydrating agent, removing a water molecule from ethanol.
Chemical Equation: CH3CH2OHConc.[citestart]H2SO4,443KCH2=CH2+H2O (iv) The reaction between B (CH3COOH) and C (C2H5OH) in the presence of concentrated H2SO4 is an esterification reaction.
Chemical Equation: CH3COOH+C2H5OHConc.[citestart]H2SO4CH3COOC2H5+H2O
Major product: The major product formed is ethyl ethanoate (CH3COOC2H5), which is an ester.
Use: Esters are used in making perfumes and flavouring agents due to their pleasant, fruity smell.

28 (i) Describe the various steps involved in the process of binary fission with the help of a diagram. (ii) Why do multicellular organisms use a complex way of reproduction?

(i) Binary fission is a type of asexual reproduction where a single parent cell divides into two identical daughter cells.

Step 1: The cell, such as in amoeba, elongates and the nucleus divides by mitosis.
Step 2: The cytoplasm divides, and a constriction forms in the middle of the cell.
Step 3: The constriction deepens, eventually splitting the parent cell into two new, identical daughter cells. (ii) Multicellular organisms use a more complex way of reproduction because they are not just a random collection of cells. They have specialized cells, tissues, and organs that perform specific functions. This complex body design means that simple cell division is not an effective way to reproduce the whole organism. Instead, they require specialized reproductive organs and cells to produce gametes and form a new, complete organism.

28 (i) Describe the role of prostate gland, seminal vesicle and testes in the human male reproductive system. (ii) How is the surgical removal of unwanted pregnancies misused? (iii) Explain the role of oral contraceptive pills in preventing conception.

(i) The roles of the different parts of the male reproductive system are:

Testes: Produce sperm and the male hormone testosterone.
Seminal Vesicle: Secretes a fluid that nourishes the sperm and makes their transport easier. This fluid is rich in fructose for energy.
Prostate Gland: Secretes a fluid that helps to neutralize the acidity of the urethra and provides nourishment and mobility for the sperm. The secretions from the seminal vesicles and prostate gland combine with sperm to form semen. (ii) The surgical removal of unwanted pregnancies, also known as Medical Termination of Pregnancy (MTP), is misused to perform female foeticide. In some cases, the gender of the foetus is determined, and if it is female, the pregnancy is terminated. This is a gross violation of medical ethics and leads to an imbalance in the male-to-female ratio in society. (iii) Oral contraceptive pills contain hormones (estrogen and progesterone) that prevent ovulation. They inhibit the release of eggs from the ovaries, so no egg is available for fertilization. They also make the uterine lining unsuitable for implantation and can thicken cervical mucus, making it difficult for sperm to enter the uterus.

29 (i) Consider a conductor of resistance ‘R’, length ‘L’, thickness’d’ and resistivity ‘p’. Now this conductor is cut into four equal parts. What will be the new resistivity of each of these parts? Why? (ii) Find the resistance if all of these parts are connected in: (a) Parallel (b) Series (iii) Out of the combinations of resistors mentioned above in the previous part, for a given voltage which combination will consume more power and why?

(i) The new resistivity of each of the four equal parts will remain ρ (rho). Resistivity is an intrinsic property of the material of the conductor and does not depend on its length or thickness.

(ii) When the conductor is cut into four equal parts, the length of each part becomes L/4. Since resistance is directly proportional to length (R ∝ L), the resistance of each individual part will be

R1=R/4.

(a) Parallel combination: The equivalent resistance (Req) is given by: 1/Req=1/R1+1/R2+1/R3+1/R4 1/Req=1/(R/4)+1/(R/4)+1/(R/4)+1/(R/4) 1/Req=4/R+4/R+4/R+4/R=16/R

Req=R/16

(b) Series combination: The equivalent resistance (Req) is given by: Req=R1+R2+R3+R4

Req=R/4+R/4+R/4+R/4=4R/4=R

(iii) For a given voltage, the

parallel combination will consume more power. Power (P) is calculated using the formula

P=V2/R. Since the voltage (V) is constant, power is inversely proportional to resistance (P ∝ 1/R). The equivalent resistance in the parallel combination (

R/16) is much lower than the equivalent resistance in the series combination (R). A lower resistance will result in higher power consumption.

30 (i) A lens produces a magnification of -0.5. Is this a converging or diverging lens? If the focal length of the lens is 6 cm, draw a ray diagram showing the image formation in this case. (ii) A girl was playing with a thin beam of light from a laser torch by directing it from different directions on a convex lens held vertically. She was surprised to see that in a particular direction, the beam of light continues to move along the same direction after passing through the lens. State the reason for her observation. Draw a ray diagram to support your answer.

(i) The magnification (m) is negative (m = -0.5), which indicates that the image formed is real and inverted. This type of image is always formed by a converging lens (convex lens). The magnification value (m = -0.5) also suggests that the image is smaller than the object and the object is placed beyond 2f.

Focal length (f) = 6 cm. The object is placed beyond 12 cm. (ii) The girl’s observation happened when the laser beam passed through the optical center of the convex lens. Light rays passing through the optical center of a lens travel undeviated, meaning they do not change their direction.

30 (i) On entering in a medium from air, the speed of light becomes half of its value in air. Find the refractive index of that medium with respect to air? (ii) A glass slab made of a material of refractive index n1 is kept in a medium of refractive index n2. A light ray is incident on the slab. Draw the path of the rays of light emerging from the glass slab, if (i) n1>n2 (ii) n1=n2 (iii) n1<n2.

(i) The refractive index (n) of a medium is the ratio of the speed of light in a vacuum (or air) to the speed of light in that medium.

Speed of light in air (c1) = v
Speed of light in the medium (c2) = v/2
Refractive Index (n) = c1/c2=v/(v/2)=2. The refractive index of the medium with respect to air is 2. (ii) The path of the light rays will depend on the relationship between the refractive indices of the glass slab (n1) and the surrounding medium (n2).
Case 1: n1>n2 The light ray will bend away from the normal as it exits the glass slab and enters the medium with a lower refractive index.
Case 2: n1=n2 The light ray will pass through the glass slab without any bending or deviation, as there is no change in refractive index.
Case 3: n1<n2 The light ray will bend towards the normal as it exits the glass slab and enters the medium with a higher refractive index.

pictiures are missing in question also and in ans also

3(d) Based on the data represented in the graph below, which of the two cities A or B would be an ideal location for establishing a wind-farm and why?

City A would be the ideal location for a wind farm. This is because the graph shows that City A has a consistently high wind speed throughout the year, while City B’s wind speed fluctuates significantly and is very low for several months. To be a good location for a wind farm, the wind speed must be high and stable to ensure continuous power generation.

Punnett Square for F2 Generation: | | P | p | | :— | :— | :— | | P | PP | Pp | | p | Pp | pp |

Parental Generation (P):

Parent 1: Purple flowers (PP)
Parent 2: White flowers (pp)
Gametes: P and p

F1 Generation:

Cross: PP x pp
Resulting Genotype: All offspring are Pp
Visible Character (Phenotype): All plants have purple flowers, as the dominant P allele masks the recessive p allele.

F2 Generation:

Cross: F1 x F1 (Pp x Pp)
Gametes: P, p and P, p
Resulting Genotypes:
- PP (25%)
- Pp (50%)
- pp (25%)
Visible Characters (Phenotypes):
- 3/4 (75%) of the plants have purple flowers (PP and Pp genotypes)
- 1/4 (25%) of the plants have white flowers (pp genotype)

(i) To obtain an erect image using a concave mirror, the object must be placed between the pole (P) and the principal focus (F). Since the focal length is 12 cm, the range of the object distance should be less than 12 cm. (ii) In this case, the image will be larger than the object and will be virtual and erect.

Licensed by Google

(iii) If the object is placed 24 cm in front of the mirror, the object is at the center of curvature (C), because the radius of curvature (R) is twice the focal length (R=2f=2×12 cm=24 cm). Therefore, the image will also be formed at the center of curvature (C), which is 24 cm in front of the mirror. The image will be real, inverted, and of the same size as the object.

The circuit diagram should show the following:

A main power supply coming into the house.
A fuse or circuit breaker connected in series with the live wire for safety.
An earthing connection for safety, which connects to the metal casing of the appliances like the refrigerator and the plug point.
The electric bulb, electric fan, refrigerator, and plug point connected in parallel to the main supply. This ensures that each appliance gets the full voltage and can be operated independently.

Licensed by Google

(i) The phenomenon is called dispersion of light. (ii) The colour seen at X will be Violet and the colour seen at Y will be Red. (iii) Different colours of white light bend at different angles because each colour has a different wavelength. The refractive index of the prism material is different for different wavelengths of light. Red light has the longest wavelength and is bent the least, while violet light has the shortest wavelength and is bent the most.

(i) The saturated hydrocarbon is D (C2H6). Saturated hydrocarbons have only single bonds between carbon atoms. A (C2H4) is an unsaturated hydrocarbon (alkene) with a double bond. (ii) The organic acid is B (CH3COOH), which is ethanoic acid (or acetic acid).

Structural Formula:

(iii) Compound C (C2H5OH) (ethanol) when heated at 443K with concentrated H2SO4 forms ethene (C2H4).

Role of Concentrated H2SO4: It acts as a dehydrating agent, removing a water molecule from ethanol.
Chemical Equation: CH3CH2OHConc.H2SO4,443KCH2=CH2+H2O (iv) The reaction between B (CH3COOH) and C (C2H5OH) in the presence of concentrated H2SO4 is an esterification reaction.
Chemical Equation: CH3COOH+C2H5OHConc.H2SO4CH3COOC2H5+H2O
Major product: The major product formed is ethyl ethanoate (CH3COOC2H5), which is an ester.
Use: Esters are used in making perfumes and flavouring agents due to their pleasant, fruity smell.

28 (i) Describe the various steps involved in the process of binary fission with the help of a diagram. (ii) Why do multicellular organisms use a complex way of reproduction?

(i) Binary fission is a type of asexual reproduction where a single parent cell divides into two identical daughter cells.

Step 1: The cell, such as in amoeba, elongates and the nucleus divides by mitosis.
Step 2: The cytoplasm divides, and a constriction forms in the middle of the cell.
Step 3: The constriction deepens, eventually splitting the parent cell into two new, identical daughter cells.

(ii) Multicellular organisms use a more complex way of reproduction because they are not just a random collection of cells. They have specialized cells, tissues, and organs that perform specific functions. This complex body design means that simple cell division is not an effective way to reproduce the whole organism. Instead, they require specialized reproductive organs and cells to produce gametes and form a new, complete organism.

Focal length (f) = 6 cm. The object is placed beyond 12 cm.

(ii) The girl’s observation happened when the laser beam passed through the optical center of the convex lens. Light rays passing through the optical center of a lens travel undeviated, meaning they do not change their direction.

(i) The refractive index (n) of a medium is the ratio of the speed of light in a vacuum (or air) to the speed of light in that medium.

Speed of light in air (c1) = v
Speed of light in the medium (c2) = v/2
Refractive Index (n) = c1/c2=v/(v/2)=2. The refractive index of the medium with respect to air is 2. (ii) The path of the light rays will depend on the relationship between the refractive indices of the glass slab (n1) and the surrounding medium (n2).
Case 1: n1>n2 The light ray will bend away from the normal as it exits the glass slab and enters the medium with a lower refractive index.
Case 2: n1=n2 The light ray will pass through the glass slab without any bending or deviation, as there is no change in refractive index.
Case 3: n1<n2 The light ray will bend towards the normal as it exits the glass slab and enters the medium with a higher refractive index.

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Class 9:

Class 8:

Class 7:

Class 7 Science – Oxford Solutions

Class 6:

Class 6 Science – Oxford Solutions