English (Part – B) (General studies) NDA/NA SOLVED PAPER 2019 (II) (51 to 100)

Total Questions: 50

1. A thin disc and a thin ring, both have mass M and radius R. Both rotate about axes through their centre of mass and are perpendicular to their surfaces at the same angular velocity. Which one of the following statements is correct?

Correct Answer: (a) The ring has higher kinetic energy.
Solution:

2. Let there be an object having some chemicals in it. It starts moving with a uniform velocity v and a chemical reaction starts happening. In this case, which of the following statement(s) is/are correct?

1. Chemical reactions happening in the system cannot change the velocity (v) of the centre of mass of the object.
2. Chemical reactions happening in the system cannot change kinetic energy of the particles inside with respect to the centre of mass of object.
Select the correct answer using the code given below:

Correct Answer: (a) Only 1
Solution:

A chemical reaction is an internal process, so there is no change in momentum and mass (since, mass is conserved in a chemical reaction). But in a chemical reaction, the kinetic energy of the particle is changes with respect to centre of mass of whole body. Hence, statement 1 is correct are stakines 2 is incorrect.

3. In which of the following phenomena do heat waves travel along a straight line with the speed of light?

Correct Answer: (c) Thermal radiation
Solution:

Thermal radiations are heat waves (infrared waves) which are electromagnetic waves. Electromagnetic waves travel in straight line with the speed of light. It depends on the temperature of the body and nature of radiating surface of the body. Hence, option (c) is correct.

4. Which one of the following statements regarding Ohm’s law is not correct?

Correct Answer: (d) All homogeneous materials obey Ohm’s law irrespective of whether the field is within range or strong.
Solution:

Statement (d) is not correct, because in strong electric field, heating effect will dominant and here is deviations of curve, i.e. it does not obey Ohm’s law.

5. When a ball bounces off the ground, which of the following changes suddenly? (Assume no loss of energy to the floor)

Correct Answer: (b) Its momentum
Solution:

When a ball bounces off the ground, there will be sudden change in the momentum of the ball.
● It includes the mass and the velocity of the object.
● It shows the sudden change of the velocity of the object according to its mass.
● If the mass is large, the change will be greater and if it is small, then the velocity will be lesser.

6. Which one of the following compounds does not exhibit a different oxidation number of the same element?

Correct Answer: (c) Fe₂O₃
Solution:

Among the given species/ compounds, only Fe₂O₃ does not exhibit
different oxidation number of Fe, in this species can be calculated as :
Let x be the O.N. of Fe.
∴ 2x + 3(-2) = 0, x = + 3
Hence, Fe is in only + 3 oxidation state in Fe₂O₃, whereas in rest of the species, the same metal exhibits different oxidation states.

7. Which one of the following statements about glass is not correct?

Correct Answer: (c) Soda glass is harder than pyrex glass.
Solution:

Pyrex glass is harder than soda lime glass. This is because, pyrex glass, (a particular blend of borosilicate glass) has a higher proportion of silicone dioxide than soda lime glass. Due to which, pyrex glass does not expand on heating, while soda lime glass is not likely to be directly and strongly heated. Thus, the high heating tolerance of pyrex glass makes it harder than soda lime glass. Hence, option (c) is incorrect. Rest of the given statements are correct.

8. Which one of the following statements is correct?

Correct Answer: (d) Boiling is a bulk phenomenon, but evaporation is a surface phenomenon.
Solution:

Boiling is a bulk phenomenon, but evaporation is a surface phenomenon is the correct statement. This is because, during evaporation, the high energy molecules from the liquid go into the gaseous phase only through the surface.
While, in boiling, the vaporisation occurs throughout the bulk of the liquid and the vapours expand freely into the surrounding.

9. Which one of the following statements about diamond and graphite is not correct?

Correct Answer: (b) Both physical and chemical properties of diamond and graphite are different.
Solution:

Statement given in option (b) is incorrect. The correct statement is, the physical properties of both diamond and graphite are same. But, as the both diamond and graphite are allotropes of same element (carbon). Thus, they both exhibits similar chemical properties. So, option (b) is the correct answer.

10. The raw materials used for the manufacture of Portland cement are:

Correct Answer: (c) lime, silica and alumina
Solution:

The raw materials used for the manufacture of Portland cement are lime, clay (provides alumina and silica) and gypsum. Thus, the correct option is (c).