NCERT Science Major Test Model Paper Class 7 2020 Questions and Answers Part 3 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Section-B: Chemistry

12. The rearing and management of silkworms for the production of silk is referred to as

(1) Maricultural

(2) Silviculture

(3) Sericulture

(4) Floriculture

Ans: Option (3)

13. Which of the following statements is not correct?

(1) Acids turns blue litmus red.

(2) Bases are bitter in taste

(3) Neutralization reaction gives salt and water

(4) All the indicators change colour in acids

Ans: Option (4)

14. Which of the following methods cannot be used to prevent rusting?

(1) Painting

(2) Alloying

(3) Galvanization

(4) Keep in moist air

Ans: Option (4)

15. In plant, water is essential for

(1) Synthesis of food

(2) Transport of nutrients

(3) Germination of seeds

(4) All of these

Ans: Option (4)

16. Assertion: Cooking oil and fats should not be thrown down the drains.

Reason: Cooking oil and fats get harden and block the drain pipes.

(1) Both assertion and reason are correct, and reason is the correct explanation of assertion.

(2) Both assertion and reason are correct, but reason is not the correct explanation of assertion.

(3) Assertion is correct, and reason is incorrect.

(4) Both assertion and reason is incorrect.

Ans: Option (1)

17. What are drip irrigations?

Ans:

  • Instead of filling up the entire field with water, farmers can be taught the method of watering the roots of plants drop by drop.
  • This method of watering the roots of the plants drop by drop is called drip irrigation.

18. (a) Name the acid present in vinegar.

(b) Enlist four important characteristics of wool.

Ans:

(a) Acetic acid is present in vinegar.

(b) Characteristics of wool (any four)

  • Wool insulates against heat and cold.
  • Wool is water repellent.
  • Wool is fire resistant.
  • Wool is elastic.
  • Wool is versatile.
  • Wool resists static electricity.
  • Wool insulates against noise.
  • Wool resists dirt.
  • Wool is fashionable.
  • Wool dyes beautifully.

19. (a) What is sludge?

(b) Explain briefly rainwater harvesting.

Ans:

(a) The solids like faeces which settle at the bottom of sedimentation tank and are removed with a scraper are called as sludge.

(b)

  • In simple terms, rainwater harvesting is a method of direct collection of rainwater from roof tops of buildings. It can be done on the roof tops of our houses as well as industries.
  • The rainwater collected can be stored for direct use or can be allowed to reach the groundwater.
  • Once the water reaches the groundwater, water table is raised. Rainwater harvesting is, therefore, a solution to the problem of depleting groundwater.

20. Breaking of an egg is a physical change while boiling of an egg is a chemical change, why?

Ans:

  • When an egg is broken, no new substance is formed hence it is a physical change but when egg is boiled, chemical nature of the egg changes.
  • The properties of a boiled egg are totally different from the raw egg. Hence, boiling of an egg is a chemical change.

21. (a) What are manholes?

(b) What kind problems people have to face due to water scarcity?

(c) Name two chemicals used to disinfect water.

(d) Name any two water-borne diseases.

Ans:

(a) A manhole is a hole, usually with a cover, through which a person may enter a sewer or drain to fix the faulty pipes.

(b) Due to water scarcity:

  • Crop production is affected, which may cause insufficient supply of food.
  • People have to walk miles to fetch water.
  • People have to stand in long queues to get their daily water.
  • People may drink dirty water which can cause water borne diseases like cholera, dysentery, typhoid, etc.
  • People may have to buy water at high prices.

(c) Addition of chlorine and exposure to ultraviolet light disinfects water.

(d) Typhoid, cholera, dysentery, etc. are water-borne diseases.

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