$$S{O_2}$$ is the component of classical smog ( i.e.; reducing smog ) while unsaturated hydrocarbons, nitrogen oxides and ozone are the components of photochemical smog ( i.e.; oxidising smog ).
62.
Which causes death of fishes in water bodies polluted by sewage ?
$$C{O_2}$$ present in normal concentration is not an air pollutant. However, when $$C{O_2}$$ level increases in atmosphere, it results in global warming.
64.
Organic matter is considered as a major source of water pollution caused by wastes of food, animal and human excreta, garbage etc. The excess of organic matter in water causes a threat to aquatic life because
A
the space available to aquatic life decreases
B
microorganisms consume dissolved oxygen to decompose organic matter
C
organic matter is swallowed by small animals
D
decomposition of organic matter increases the temperature of water
Answer :
microorganisms consume dissolved oxygen to decompose organic matter
If a lot of organic matter is decomposed, a lot of dissolved oxygen is consumed by microorganisms hence dissolved oxygen is no longer available for aquatic life.
65.
Which one of the following depletes ozone layer ?
The amount of $$BOD$$ in water is the measure of the amount of organic matter in water in terms of how much oxygen is required to break it down biologically.
68.
Which of the following statements about polar stratosphere clouds $$(PSCs)$$ is not correct ?
A
$$PSCs$$ do not react with chlorine nitrate and $$HCl.$$
B
Type $$I$$ clouds are formed at about $$ - {77^ \circ }C$$ and contain solid $$HN{O_3}.3{H_2}O.$$
C
Type $$II$$ clouds are formed at about $$ - {85^ \circ }C$$ and contain some ice.
D
A tight whirlpool of wind called Polar Vortex is formed which surrounds Antarctica.
Answer :
$$PSCs$$ do not react with chlorine nitrate and $$HCl.$$