51. The function of skimming tank in sewage treatment is to remove __________ substances.
52. Sooty and sulphurous smog formed due to combustion of fossil fuels particularly in winter, continues throughout the day and night. When the moist atmospheric air's water vapor condenses on the solid particles of smoke thereby forming smog (smoke + fog), it causes
53. Threshold Limit Value (TLV) is the maximum allowable concentration (i.e. safe limit) of pollutants in air. Safe limit for SO2 in air is __________ ppm.
54. In sewage treatment, its sedimentation is speeded up by commonly adding
55. Atmospheric pollution caused by the exhaust gas of supresonic transport air-crafts is mostly in the atmospheric region called
56. Noise level heard inside a bus in busy city traffic or inside a sub-way train corresponds to about __________ decibels.
57. Out of the following, TLV of __________ is the minimum (about 0.02 ppm).
58. Limestone powder is injected during pulverised coal burning in boilers to __________ the flue gases.
59. Sound produced by an automobile horn heard at a distance of 1.5 metres corresponds to about __________ decibels.
60. Noise level audible to audience sitting in the 5th row from the stage during a large orchestra show corresponds to about __________ decibels.
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