General Ability NDA/NA Solved Paper 2020-I (101-150)

Total Questions: 50

41. The Sun appears reddish during sunrise and sunset. The phenomenon in optics which is responsible for this appearance of the Sun is

Correct Answer: (c) Scattering
Solution:

It is due to scattering of light. During sunrise and sunset, the sun is at the longest position. Here blue light gets scattered off and due to larger wavelength ofthe red light it can travel a longer distance and hence reach our eyes. This we see the sun red. But at noon, the sun is at
the nearest point to earth. Hence all the colors get scattered almost equally and this you see white light.

42. A lens has a power of +2.0 Dioptre. Which one of the following statements about the lens is true?

Correct Answer: (c) The lens is convex and has a focal length of 0.5 metre
Solution:

A dioptre, is a unit of measurement of the optical power of a lens, which is equal to the reciprocal of the focal length measured in meters (that is, 1/f metres). It is thus a unit of reciprocal length.
Hence, P=1/f ⇒2=1/f⇒f=0.5 meter.
As the value is positive, it is a positive lens, that is, convex.
Hence, the option (c) is true.

43. At nearly 70°C, sodium bicarbonate shows the property of gradually decomposing, which makes it usable in bakery products. The product of decomposition responsible for this use of sodium bicarbonate is

Correct Answer: (a) Carbon dioxide
Solution:

Above 70°C, sodium bicarbonate gradually decomposes into sodium carbonate, water and carbon dioxide as follows - 2 NaHCO₃-Na₂CO₃+H₂O+ CO₂, In bakery, it reacts with
other components or decomposes at higher temperature to release carbon dioxide, which causes dough to rise.

44. Number of molecules of water of crystallization in copper sulphate, sodium carbonate and Gypsum are

Correct Answer: (a) 5, 10 and 2 respectively
Solution:

Copper Sulphate: CuSO₄.5H₂O
Sodium Carbonate: NA₂CO₃.10H₂О
Gypsum: CaSO₄.2H₂O
The number of molecules of water of crystallization in copper sulphate is 5, Sodium caibonate is 10 while in Gypsum it is 2.

45. Which one of the following is the correct sequence of change in colours when a turmeric stain on white clothes is scrubbed by soap and then washed with water?

Correct Answer: (b) Yellow - reddish brown- yellow
Solution:

Soaps are basic in nature therefore when rubbed on turmeric stain on white cloths. Yellow colour ofvturmeric changes to redish brown. The correct sequence of change
in colour is;
Yellow ---- Redish brown ---- Yellow

46. Which one of the following statements regarding Bleaching powder and D.D.T. is correct?

Correct Answer: (c) Both contain chlorine
Solution:

Dichlorodiphenyl trichloroethane (DOT) (organic compound)
Bleaching Rowder CaOCl₂ calcium hypochlorite (Inorganic compound)
Both contains chlorine as it is evident from formula/structure.

47. Which one of the following is the best example of desiccant?

Correct Answer: (a) Silica gel
Solution:

Desiccants are compounds or agents, such as Montmorillonite Clay or Silica Gel, used in facilitating low humidity environments by absorbing moisture content from the air. Typically used in transport, storage or maintenance of materials and products, desiccants are
used to keep everything from gym shoes to military munitions dry. The most common desiccant is silica gel.

48. Which one of the following was the first mineral acid discovered?

Correct Answer: (c) Nitric acid
Solution:

The first mineral acid to be discovered was nitric acid. It was discovered in the 13th century by the alchemist Jabir ibn Hayyan (also known as Geber), who is credited with the early development of many chemical substances and methods.

49. Solve the following question?

Correct Answer: (a)
Solution:

50. In case of a concave mirror, if an object is kept between principal focus F and pole P ofthe mirror, then which one of the following statements about the image is NOT correct?

Correct Answer: (c) The image will be formed at infinity
Solution:


Image formed virtual, erect, magnified and behind the mirror.