SOLVED PAPER 2020 (CDS) (I) (General Studies)

Total Questions: 120

11. If the speed of light in air is 3×10⁸ m/s, then the speed of light in a medium of refractive index 3/2 is

Correct Answer: (a)
Solution:Given, speed of light in air 3×10⁸ m/s

12. Which one of the following types of radiation has the shortest wavelength ?

Correct Answer: (d) Ultraviolet (UV)
Solution:Decreasing order of wavelength of Electromagnetic waves are :

Radio waves > Infrared (IR) > Visible light > Ultraviolet (UV)

13. The unit of the force constant k of a spring is

Correct Answer: (b) N/m
Solution:The unit of force constant k of a spring is N/m. According to Hooke’s law, force applied by spring,

F = - kx or , k = - (f/x)

where, k is a constant that is a characteristic of the spring known as spring constant or force constant and x is the final elongation of the spring.

14. Which one of the following is not an epidemic disease?

Correct Answer: (c) Smallpox
Solution:Smallpox is not an epidemic disease. An epidemic is the rapid spread of an infectious disease to a large number of people in a given population within a short period of time, usually two weeks or less. Malaria and elephantiasis both are vector (Mosquito) borne diseases, thus during favourable conditions like flood or heavy rain, the sudden increase in numbers of mosquito will also cause outbreak of these diseases.

Similarly, cholera is also an epidemic disease as it is water borne disease, thus presence of bacteria Vibrio cholerae in local water source like pond or well will cause outbreak of cholera in every member of locality in a short period of time.

A pandemic is an epidemic of world-wide proportions i.e. outbreaks of these diseases occur across international borders, e.g. smallpox, which throughout history, has killed between 300-500 million people in all over the world.

15. Which one of the following animals has a three-chambered heart?

Correct Answer: (b) Salamander
Solution:Amphibians and reptiles, such as salamanders, frogs, toads, lizards and snakes, have three-chambered heart, one ventricle and two atria. In three-chambered heart, blood from the ventricle travels to the lungs and skin where it is oxygenated and also to the body. In the ventricle, deoxygenated and oxygenated blood are mixed before being pumped out of the heart. Scoliodon has two-chambered heart, while pigeon and human beings have four-chambered heart.

16. Which one of the following is the correct sequence of events during sexual reproduction in plants?

Correct Answer: (c) Pollination, fertilisation, division of zygote, formation of embryo, seedling
Solution:In flowering plants during sexual reproduction following events occur
  • Formation of Flower which is the sexual organ of plant.
  • Gametogenesis in which pollen grains are formed in anther, while ovules are formed in ovary.
  • Pollination in which pollen grains transferred to style of gynoecium/Pistil through various means like air, water, insects, etc.
  • Fertilisation Where a haploid male gamete fuses with another haploid egg cell of embryo sac of ovule.
  • Embryogenesis After fertilisation a diploid zygote is formed, which develops into a multicellular embryo through repetitive cell divisions.
  • Formation of Seed and Seedling After maturation the embryo develops into seed. The dormant seed after germination is known as seedling, which give rise to a new young plant.

17. When air is blown from mouth into a test-tube containing limewater, the limewater turns milky. This is due to the presence of

Correct Answer: (c) carbon dioxide
Solution:The lime water[Ca(OH)₂] is turned into milky due to formation of calcium carbonate when the lime water reacts with carbon dioxide. The products formed in this reaction is calcium carbonate (CaCO₃) and water. The reaction is given below

18. Which one of the following is the ‘energy currency’ for cellular processes?

Correct Answer: (b) ATP
Solution:During the process of oxidation of food within a cell, all the energy contained in the respiratory substrates is not released free into the cell, or in a single step. Instead, it is released in a series of stepwise reactions controlled by enzymes and is trapped as chemical energy in the form of Adenosine Triphosphate (ATP).

Thus, it is said that ATP acts as the energy currency of the cell. The energy trapped in ATP is used in many energy requiring biological processes of the organisms such as locomotion, digestion, thinking, etc. During aerobic respiration, most of the ATPs are formed in mitochondria.

19. Which one of the following is the first enzyme to mix with food in the digestive tract?

Correct Answer: (d) Amylase
Solution:Amylase is the first enzyme which mix with food in the digestive tract. The mastication of food in mouth is the first event of digestion in alimentary canal or digestive tract. During this process, digestion starts in the oral cavity by hydrolytic action of enzyme salivary amylase.

The saliva secreted into oral cavity contains two enzymes, i.e. amylase and lysozyme. About 30% of the starch gets hydrolysed in the oral cavity by the action of salivary amylase (at optimum pH 6.8) into a disaccharide, i.e. maltose.

Lysozyme acts as an antibacterial agent. It kills bacteria thus prevents infections.

20. Mahatma Gandhi’s Dandi March, a great event in Indian freedom struggle, was associated with

Correct Answer: (b) sodium chloride
Solution:Mahatma Gandhi’s Dandi March, a great event in Indian freedom struggle was associated with sodium chloride.