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Class X – Science Practice Paper – 1 – Answers

Subject: Science

Grade: X

Time: 90 mins

Marks: 30

General Instructions:

  • The question paper comprises of three Sections A, B and C
  • All questions are compulsory
  • Questions 1 to 5 in Section A are multiple choice questions of one mark each.
  • Questions 6 to 16 in Section B and C are two marks and three marks questions.

Section A

1. NaCl + AgNO3 — > AgCl + NaNO3

The above reaction can be categorized into which of the following type?

a) Displacement reaction

b) Combination reaction

c) Double displacement reaction

d) None of these

View Answer

Ans. (c)

2. Which of the following reactions will not take place?

a) Zn + CuSO4 —- > ZnSO4 + Cu

b) 2Pb(NO3)2 + Mg —- > 2Pb + Mg(NO3)2

c) 3Mg + Al2(SO4)3 —- > 3MgSO4 + 2Al

d) ZnSO4 + Fe —- > Zn + FeSO4

View Answer

Ans. (d)

3. When crystals of lead nitrate are heated strongly in a dry test tube.

a) crystals immediately melt

b) a brown residue is left

c) white fumes appear in the tube.

d) a yellow residue is left.

View Answer

Ans. (d)

4. The image formed by a concave mirror is observed to be real, inverted and larger than the object. Where should be the position of the object?

a) Between the principal focus and the centre of curvature

b) At the centre of curvature

c) Beyond the centre of curvature

d) Between the pole of the mirror and its principal focus.

View Answer

Ans. (a)

5. The image shows the digestive system of human beings.

Which of these correctly represent the labels B, C, D and E?

a) B – Oesophagus, C – Liver, D – Stomach, E – pancreas

b) B – Pancreas, C – Oesophagus, D – Liver, E – Stomach

c) B – Stomach, C – Pancreas, D – Oesophagus, E – Liver

d) B – Liver, C – Stomach, D – Pancreas, E – Oesophagus

View Answer

Ans. (a)

Section – B

6. Write balanced chemical equations for the following reactions:

(i) Silver bromide on exposure to sunlight

View Answer

Ans. 2AgBr ——- > 2Ag + Br2  (In presence of sunlight)

(ii) Sodium sulphate solution is added to Barium chloride solution to form sodium chloride and barium sulphate.

View Answer

Ans. Na2SO4 + BaCl2 ——- > 2NaCl + BaSO4

7. Observe the given experimental set up and answer the questions in the box

a) Name the gas evolved in the given experiment. Is it an exothermic or endothermic reaction?

View Answer

Ans. Hydrogen gas. Exothermic reaction.

b) Write chemical equation for the reaction involved.

View Answer

Zn + H2SO4 ——- > ZnSO4 + H2

8. How can you distinguish between plane mirror, convex mirror and concave mirror by merely looking at the image formed in each case?

View Answer

Ans. In case of plane mirror, the image is of the same size as the object.

In case of concave mirror, the image is magnified

In case of convex mirror, the image is diminished

9. a) An object is placed 20 cm in front of a concave mirror of focal length 10 cm. Find the distance from the mirror at which a screen should be placed in order to obtain a sharp image. What is the nature of the image?

View Answer

Ans. Here h = 2.0 cm

u = -20.0 cm

f = -10.0 cm

1/v = 1/f – 1/u

= 1/(-10)  – 1/(-20)

= -1/10 + 1/20 = -1/20

v = -20 cm

Again h2/h1 = -v/u

h2 = -(-20)/(-20) x 2.0 = -2.0 cm

Hence an image of length 2.0 cm is formed in front of mirror at a distance of 20 cm. The –ve sign of v and h show that the image is real and inverted image.

b) Write any two uses of concave mirror in daily life?

View Answer

Ans. i) It is used as a shaving mirror.

(ii) It is used as reflector in torch, head light of automobiles.

10. An object 3 cm high is placed at a distance of 9cm in front of a concave mirror of focal length 18 cm. Find the position and the size of image formed.

View Answer

Ans. h1 = 3 cm

h2 = ?

1/f = 1/v + 1/u

1/v = 1/f – 1/u

= 1/(-18) + 1/9 = 1/18

v = 18 cm

m = -v/u = h2/h1

-18/9 = h2/3

h2 = -6 cm

So the image formed is real, inverted and larger than the size of the object

11. Bile juice does not have any digestive enzyme but still plays a significant role in the process of digestion. Justify the statement.

View Answer

Ans. Bile juice makes the acidic food coming from the stomach alkaline for the action of pancreatic enzymes. Bile salts break the large globules of fat in the intestine to smaller globules increasing the efficiency of enzyme action. This is similar to the emulsifying action of soaps on dirt.

12. a) How does an amoeba obtain its food?

View Answer

Ans. In Amoeba, a cell membrane invagination (pseudopodia) surround the food particle. This is followed by formation of food vacuole surrounding the food by joining of pseudopodia of both sides and engulfment of food vacuole in animal body. Also known as phagosomes, these food vesicles serve as site of food digestion.

b) In the experiment “Light is essential for photosynthesis”, why does the uncovered part of the leaf turn blue-black after putting iodine solution?

View Answer

Ans. In the experiment, light is essential for photosynthesis, the uncovered region of the leaf, receives sunlight and performs photosynthesis. The leaf, therefore turns blue-black after putting iodine in this area due to the production of starch.

13. a) How is the small intestine designed to absorb digested food.

View Answer

Ans. The small intestine has millions of tiny finger-like projections called villi. These villi increase the surface area for efficient food absorption. Within these villi, many blood vessels are present that absorb the digested food and carry it to the bloodstream.

b) If we chew chapatti for long after some time it tastes sweet? Why is this so?

View Answer

Ans. It breaks down starch in bread into simpler sugars (maltose) which give a sweet taste, since you are chewing for a longer while, more time and more mixing, for enzymatic action and hence you perceive it as sweet.

Section C

14. a) What is observed when a solution of potassium iodide solution is added to a solution of lead nitrate? Name the type of reaction.

View Answer

Ans. When a solution of potassium iodide is added to a solution of lead nitrate taken in a test tube, the precipitation of a yellowish solid is observed. This yellowish solid is lead iodide. Potassium nitrate is formed along with lead iodide. This is a double displacement reaction.

b) What is the chemical name of slaked lime? How is it prepared?

Ca(OH)2 – Calcium Hydroxide

It is prepared when quicklime (calcium oxide) is mixed or slaked with water.

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c) Respiration is an exothermic reaction. Explain.

View Answer

Ans. Because energy is released during the process of respiration; it is an exothermic process. The carbon dioxide in the meal is broken down into glucose during this process. This glucose reacts with oxygen in our cells, releasing a large amount of energy.

15. A spherical mirror produced an image of magnification -1 on a screen placed at a distance of 50 cm from the mirror.

a) Write the type of mirror

View Answer

Ans. As magnification is in negative the image will be down the principle axis compared to the object and will form in Concave Mirror.

b) Find object distance

View Answer

Ans. The distance of image from the object is zero, real and inverted image of the same size is formed at the same place where object is placed.

c) Draw a neat and labelled ray diagram to show the image formation in this case.

View Answer

Ans.

16. a) List the three events that occur during the process of photosynthesis

View Answer

Ans. The three events that occur during the process of photosynthesis are:

(i) Absorption of light energy by chlorophyll.

(ii) Conversion of light energy to chemical energy and splitting of water molecules into hydrogen and oxygen.

(iii) Reduction of carbon dioxide to carbohydrates.

b) Draw a diagram to show open stomatal pore and label on it:

i) Guard cell

ii) Chloroplast

View Answer