51. For a steady state system, the law of conservation of mass states that:

(a) Input rate – output rate = Decay rate
(b) Input rate + output rate = Decay rate
(c) Input rate – output rate = 0
(d) Input rate + output rate = 0

Answer: (c)

52. A critical point in a river occurs where:
(a) The withdrawal rate of dissolved oxygen is faster than the reaeration rate
(b) The withdrawal rate of dissolved oxygen is slower than the reaeration rate
(c) The withdrawal and reaeration rates are equal
(d) The dissolved oxygen reaches a minimum at a particular location and time

Answer: (d)

53. 
(a) 0.18 ppm
(b) 0.20 ppm
(c) 0.22 ppm
(d) 0.25 ppm

Answer: (d)

54. The ozone which resides in:
(a) Stratosphere protect life by absorbing long-wave length ultraviolet radiations
(b) Atmosphere protect life by absorbing short-wave length ultraviolet radiations
(c) Atmosphere protect life by absorbing long-wave length ultraviolet radiations
(d) Stratosphere protect life by absorbing short-wave length ultraviolet radiations

Answer: (d)

55. The permissible limit of fluoride in drinking water as per ISI standard (IS : 10500-2003) is:
(a) 2.0 ppm
(b) 1.5 ppm
(c) 1.0 ppm
(d) 0.5 ppm

Answer: (b)

56. El - Nino phenomenon occurs due to a major shift in the atmospheric pressure as the reversal of trade winds direction over the central equatorial pacific ocean that leads to the spread of warm water towards:
(a) North
(b) South
(c) East
(d) West

Answer: (c)

57. The complex level of biodiversity is:
(a) Species biodiversity
(b) Ecosystem biodiversity
(c) Genetic biodiversity
(d) Genus biodiversity

Answer: (b)

58. The substance which is primarily responsible for raising pH of rainwater is:
(a) Carbon dioxide
(b) Sulphur dioxide
(c) Ammonia
(d) Carbon monoxide

Answer: (c)

59. The main constituents of photochemical smog are:
(a) Sulphur dioxide, Nitrogen dioxide and Nitric oxide
(b) Nitrogen dioxide, Ozone and Nitric oxide
(c) Sulphur dioxide, Ozone and Hydroflurocarbons
(d) Nitrogen dioxide, Ozone and Hydroflurocarbons

Answer: (b)

60. Due to heavy traffic in the morning, the concentration of:

Answer: (a)