(d) Burning of an electric lamp
Ans: (b)
40. The atomic number of an element represents
    (a) number of neutrons in the nucleus
    (b) number of protons and neutrons in the nucleus
    (c) the valency of the element
    (d) number of protons in the nucleus
Ans: (d)
41. Which of the following statements regarding natural radioactivity is true?
    (a) It is spontaneous disintegration of atoms
    (b) It is induced by bombardment with projectiles
    (c) It is transmutation of atoms with projectiles
    (d) It is dependent on temperature
Ans: (a)
42. Gases have
    (a) a definite shape but not volume
    (b) a definite volume and shape
    (c) a definite volume but not shape
    (d) neither definite volume nor shape
Ans: (d)
43. The most abundant constituent in air is
    (a) hydrogen
    (b) nitrogen
    (c) oxygen
    (d) noble gases
Ans: (b)
44. Ethyl alcohol is
    (a) a deliquescent substance
    (b) an efflorescent substance
    (c) a hygroscopic substance
    (d) a dehydrating substance
Ans: (c)
45. The function of nitrogen in air is
    (a) to make air a moderate supporter of combustion
    (b) to maintain the density of air constant
    (c) to prevent the hydrogen in air from exploding
    (d) to reduce the poisonous nature of ozone in air
Ans: (a)
46. One method by which the components of air can be separated is
    (a) shaking with caustic soda solution
    (b) shaking with water
    (c) fractional distillation of liquid air
    (d) passing air over heated magnesium
Ans: (c)
47. The noble gas which is present in microscopic quantities in air is
    (a) xenon
    (b) krypton
    (c) argon
    (d) helium
Ans: (a)
48. The most abundant noble gas present in air is
    (a) neon
    (b) argon
    (c) helium
    (d) krypton
Ans: (b)
49. Which one of the following gases is extremely soluble in water?
    (a) Carbon dioxide
    (b) Ammonia
    (c) Chlorine
    (d) Hydrogen sulphide