Question Paper

CBSE Board 2020

Section A

1 Mark Questions

Question 1: Define electropositivity.

OR

The atomic radii of first group elements are given below:

Group I ElementAtomic Radii (pm)
Na86
K231
Rb244
Cs282

State the reason behind the observed trend in the above elements.

Answer: When we move from top to bottom in a group, atomic radii increase because of addition of a shell in subsequent periods in a group.


Question 2: How are covalent bonds formed?

Answer: Covalent bonds are formed by sharing of electrons.

Question 3: Questions numbers 3(a) to 3(d) are based on table given below. Study the table in which the levels of Thyroid Stimulating Hormone (TSH) in women are given and answer the questions that follow on the basis of understanding of the following paragraph and the related studied concepts.

Age RangeNormal (mU/L)Low (mU/L)
18-29 years0.4-2.34< 0.4
30-49 years0.4-4.0< 0.4
50-79 years0.4-4.68< 0.46

Women are at greater risk for developing abnormal TSH levels during menstruation, while giving birth and after going through menopause. Around 5% of women in the United States have some kind of thyroid problem compared to 3% of men. Despite claims that high TSH increases your risk for heart disease, a 2013 study found no link between high TSH and heart diseases. But a 2017 study showed that older women are especially at risk for developing thyroid cancer if they have high TSH levels along with thyroid nodules.

(a) A 35 year old woman has TSH level 6.03 mU/L. What changes should she bring in her diet to control this level?

Answer: She should reduce her intake of carbohydrate and fat.

(b) When do women face a greater risk of abnormal TSH level?

Answer: During menstruation, during child birth and during menopause

(c) State the consequence of low TSH level?

Answer: Low TSH level can result in drastic weight loss and weakness

(d) Name the mineral that is responsible for synthesis of hormone secreted by thyroid gland.

Answer: Iodine

Question 4: Answer question numbers 4(a) to 4(d) on the basis of your understanding of the following paragraph and the related studies concepts.

The Tehri dam is the highest dam in India and one of the highest in the World. The Tehri dam withholds a reservoir of capacity 4.0 km3 and surface area of 52 km2. It is used for irrigation, municipal water supply and the generation of 1000 MW of hydro electricity.

The Tehri Dam has been the object of protests. Environment activist Shri Sunder Lal Bahuguna led the “Anti Tehri Dam Movement” from 1980s to 2014. The protest was against the displacement of town inhabitants and environmental consequences of the weak ecosystem. The relocation of more than 1,00,000 people from the area has led to protracted legal battles over resettlement rights and ultimately resulted in the delayed completion of the project.

(a) How is hydropower harnessed?

Answer: Water is collected in a reservoir behind the dam. The stored water is released to turn a turbine in order to produce electricity.

(b) Define 1 MW

Answer: 1 MW = 1000000 W

(c) Mention two disadvantages of constructing Tehri Dam.

Answer: Construction of Tehri Dam has resulted in large scale destruction of biodiversity in catchment area and large scale displacement of people.

(d) What happens when water from great heights is made to fall on blades of turbine?

Answer: Blades of turbine move and convert kinetic energy of water into electric energy.

Question 5: An element ‘X’ is forming an acidic oxide. Its position in modern periodic table will be

  1. Group 1 and Period 3
  2. Group 2 and Period 3
  3. Group 13 and Period 3
  4. Group 16 and Period 3

Answer: (d) Group 16 and Period 3

Explanation: Other groups contain metals and metals generally make basic oxides

OR

Consider the following statements about and element ‘X’ with number of protons 13.

  1. It forms amphoteric oxide
  2. Its valency is three
  3. The formula of its chloride is XCl3

The correct statement(s) is/are

  1. Only (i)
  2. Only (ii)
  3. (i) and (iii)
  4. (i), (ii) and (iii)

Answer: (d) (i) (ii) and (iii)

Explanation: Aluminium (13) makes amphotetic oxide, has 3 as valency and makes AlCl3


Question 6: An aqueous solution ‘A’ turns phenolphthalein solution pink. On addition of an aqueous solution ‘B’ to ‘A’, the pink colour disappears. The following statement is true for solution ‘A’ and ‘B’.

  1. A is strongly basic and B is a weak base
  2. A is strongly acidic and B is a weak acid
  3. A has pH greater than 7 and B has pH less than 7
  4. A has pH less than 7 and B has pH greater than 7

Answer: (c) A has pH greater than 7 and B has pH less than 7

Question 7: In which of the following, the identity of initial; substance remains unchanged?

  1. Curdling of milk
  2. Formation of crystals by process of crystallization
  3. Fermentation of grapes
  4. Digestion of food

Answer: (b) Formation of crystals by process of crystallization

Question 8: Several factories were pouring their wastes in rivers A and B. Water samples were collected from these two rivers. It was observed that sample collected from river A was acidic while that of river B was basic. The factories located near A and B are:

  1. Soaps and detergents factories near A and alcohol distillery near B.
  2. Soaps and detergents factories near B and alcohol distillery near A.
  3. Lead storage battery manufacturing factories near A and soaps and detergents factories near B.
  4. Lead storage battery manufacturing factories near B and soaps and detergents factories near A

Answer: (b) Soaps and detergents factories near B and alcohol distillery near A.

Question 9: A diagram of traditional water harvesting system is given below:

The statement which defines the system and its parts is

diagram of khadin
  1. This is an ideal setting of the Khadin system and A = Catchment area; B = Saline area & C = Shallow dugwell
  2. This is an ideal setting of the shallow dugwell system and A = Catchment area; B = Saline area & C = Khadin
  3. This is an ideal setting of Catchment area and A = Khadin, B = Saline area and C = shallow dugwell
  4. This is showing Saline area and A = Catchment area, B = Khadin and C = shallow dugwell

Answer: (a) This is an ideal setting of the Khadin system and A = Catchment area; B = Saline area & C = Shallow dugwell

OR

The major ill effect of mono culture practice in forests is on the

  1. Biodiversity which faces large destruction
  2. Local people whose basic needs can no longer be met from such forests
  3. Industries
  4. Forest department

Answer: (a) Biodiversity which faces large destruction


Question 10: The maximum resistance which can be made using four resistors each of resistance ‘1/2’ Ω is

  1. 2 Ω
  2. 1 Ω
  3. 2.5 Ω
  4. 8 Ω

Answer: (a) 2 Ω

Explanation: We know that equivalent resistance increases when resistors are connected in series, and is equal to sum of resistances.

Question 11: A cylindrical conductor of length ‘l’ and uniform area of cross section ‘A’ has resistance ‘R’. The area of cross section of another conductor of same material and same resistance by of length 2l is

  1. `A/2`
  2. `(3A)/2`
  3. 2A
  4. 3A

Answer: (c) 2A

Explanation: Remember that resistance varies directly are length and inversely as area of cross section of conductor.

Question 12: The sky appears dark to passengers flying at very high altitudes mainly because:

  1. Scattering of light is not enough at such heights
  2. There is no atmosphere at great heights
  3. The size of molecules is smaller than the wavelength of visible light
  4. The light gets scattered towards the earth

Answer: (a) Scattering of light is not enough at such heights

NOTE: For question numbers 13 and 14, two statements are given, one labeled Assertion (A) and the other labeled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:

  1. Both (A) and (R) are true and (R) is correct explanation of the assertion
  2. Both (A) and (R) are true but (R) is not the correct explanation of the assertion
  3. (A) is true but (R) is false
  4. (A) is false but (R) is true

Question 13: Assertion (A): Alloys are commonly used in electrical heating devices like electric iron and heater.

Reason (R): Resistivity of an alloy is generally higher than that of its constituent metals but the alloys have low melting points than their constituent metals.

Answer: (c) (A) is true but (R) is false

Question 14: Assertion (A): Following are the members of a homologous series:

CH3OH, CH3CH2OH, CH3 CH2 CH2OH

Reason (R): A series of compounds with same functional group but differing by - CH2 unit is called a homologous series.

Answer: (a) Both (A) and (R) are true and (R) is correct explanation of the assertion




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