Board Paper of Class 10 2020 Science Delhi(Set 3) - Solutions

Name a cyclic unsaturated carbon compound. VIEW SOLUTION

State an important advantage of using alternating current (a.c.) over direct current (d.c.). VIEW SOLUTION

The growing size of the human population is a cause of concern for all people. The rate of birth and death in a given population will determine its size. Reproduction is the process by which organisms increase their population. The process of sexual maturation for reproduction is gradual and takes place while general body growth is still going on. Some degree of sexual maturation does not necessarily mean that the mind or body is ready for sexual acts or for having and bringing up children. Various contraceptive devices are being used by human beings to control the size of population.
(a) List two common signs of sexual maturation in boys and girls.
(b) What is the result of reckless female foeticide?
(c) Which contraceptive method changes the hormonal balance of the body?
(d) Write two factors that determine the size of a population. VIEW SOLUTION

Human body is made up of five important components, of which water is the main component. Food as well as potable water are essential for every human being. The food is obtained from plants through agriculture.  Pesticides are being used extensively for a high yield in the fields. These pesticides are absorbed by the plants from the soil along with water and minerals and from the water bodies these pesticides are taken up by the aquatic animals and plants. As these chemicals are not biodegradables, they get accumulated progressively at each trophic level. The maximum concentration of these chemicals gets accumulated in our bodies and greatly affects the health of our mind and body.
 

(a) Why is the maximum concentration of pesticides found in human beings?
(b) Give one method which could be applied to reduce our intake of pesticides through food to some extent.
(c) Various steps in a food chain represent :

(a) Food web
(b) Trophic level
(c) Ecosystem
(d) Biomagnification

(d) With regard to various food chains operating in an ecosystem, man is a:

(a) Consumer
(b) Producer
(c) Producer and consumer
(d) Producer and decomposer

VIEW SOLUTION

Which one of the following is responsible for the sustenance of underground water?
(a) Loss of vegetation cover
(b) Diversion for high water demanding crops
(c) Pollution from urban wastes
(d) Afforestation VIEW SOLUTION

Incomplete combustion of coal and petroleum :
(A) increases air pollution.
(B) increases efficiency of machines.
(C) reduces global warming.
(D) produce poisonous gases.

The correct option is:
(a) (A) and (B)
(b) (A) and (D)
(c) (B) and (C)
(d) (C) and (D) VIEW SOLUTION

When sodium hydrogen carbonate is added to ethanoic acid a gas evolves. Consider the following statements about the gas evolved?
(A) It turns lime water milky.
(B) It is evolved with a brisk effervescence.
(C) It has a smell of burning sulphur.
(D) It is also a by-product of respiration.
The correct statements are:
(a) (A) and (B) only
(b) (B) and (D) only
(c) (A), (C) and (D)
(d) (A), (B) and (D) VIEW SOLUTION

When a small amount of acid is added to water, the phenomena which occur are:
(A) Dilution
(B) Neutralisation
(C) Formation of H₃O⁺ ions
(D) Salt formation
The correct statements are:
(a) (A) and (C)
(b) (B) and (D)
(c) (A) and (B)
(d) (C) and (D) VIEW SOLUTION

A real image is formed by the light rays after reflection or refraction when they:
(A) actually meet or intersect with each other.
(B) actually converge at a point
(C) appear to meet when they are produced in the backward direction.
(D) appear to diverge from a point.
Which of the above statements are correct?
(a) (A) and (D)
(b) (B) and (D)
(c) (A) and (B)
(d) (B) and (C)

OR

Consider the following properties of virtual images:
(A) cannot be projected on the screen
(B) are formed by both concave and convex lens
(C) are always erect
(D) are always inverted
The correct properties are:
(a) (A) and (D)
(b) (A) and (B)
(c) (A), (B) and (C)
(d) (A), (B) and (D) VIEW SOLUTION

At the time of short circuit, the electric current in the circuit :
(a) vary continuously
(b) does not change.
(c) reduces substantially
(d) increases heavily

OR

Two bulbs of 100 W and 40 W are connected in series. The current through the 100 W bulb is 1A. The current through the 40W bulb will be:
(a) 0.4 A
(b) 0.6 A
(c) 0.8 A
(d) 1 A VIEW SOLUTION

Calcium oxide reacts vigorously with water to produce slaked lime.
CaO(s) + H₂O(l) → Ca(OH)₂(aq)
This reaction can be classified as:
(A) Combination reaction
(B) Exothermic reaction
(C) Endothermic reaction
(D) Oxidation reaction
Which of the following is a correct option?
(a) (A) and (C)
(b) (C) and (D)
(c) (A), (C) and (D)
(d) (A) and (B)

OR

When hydrogen sulphide gas is passed through a blue solution of copper sulphate, a black precipitate of copper sulphide is obtained and the sulphuric acid so formed remains in the solution. The reaction is an example of a:
(a) Combination reaction
(b) Displacement reaction
(c) Decomposition reaction
(d) Double displacement reaction VIEW SOLUTION

In a double displacement reaction such as the reaction between sodium sulphate solution and barium chloride solution:
(A) exchange of atoms takes place
(B) exchange of ions takes place
(C) a precipitate is produced
(D) an insoluble salt is produced
The correct option is:
(a) (B) and (D)
(b) (A) and (C)
(c) only (B)
(d) (B), (C) and (D) VIEW SOLUTION

Two statements are given - one labelled  Assertion (A) and the other labelled Reason (R).
Assertion (A): Esterification is a process in which a sweet smelling substance is produced.
Reason (R) : When esters react with sodium hydroxide an alcohol and sodium salt of carboxylic acid are obtained.

Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
(a) Both A and R are true and R is the correct explanation of the Assertion.
(b) Both A and R are true but R is not the correct explanation of the Assertion.
(c) A is true but R is false.
(d) A is false but R is true. VIEW SOLUTION

Two statements are given - one labelled Assertion (A) and the other labelled Reason (R).

Assertion (A) : A solar cooker cooks the meal due to green house effect.
Reason (R) : The plane mirror is responsible for producing the green house effect.

Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
(a) Both A and R are true and R is the correct explanation of the Assertion.
(b) Both A and R true but R is not the correct explanation of the Assertion.
(c) A is true but R is false.
(d) A is false but R is true. VIEW SOLUTION