Answer: Option A. -> Taj mahal is made of marble
:
A
Tajmahal is made of marble $\left(CaC{O}_3\right)$which reacts withsulphuric acid of the acid rain causing pitting,decolourization and lusterless.

Answer: Option B. -> troposphere, stratosphere 
:
B
Oxygen plays a key role in troposphere whereas ozone in stratosphere.

Answer: Option A. -> Bacteria and other organisms
:
A
Pathogens are bacteria and other organisms which enter into water from domestic sewage and animal excreta.

Answer: Option B. -> below 5.6 
:
B
Acid rain containssulphuric acid, nitric acid and small amounts ofHCl and pH below5.6

Answer: Option B. -> biodegradable pollutants 
:
B
Domestic waste mostly constitutes biodegradable pollutants

Answer: Option D. -> oxygen gas
:
D
Oxygen gas is not agreen house gas

Answer: Option B. -> PAN   
:
B
PAN (Peroxyacetyl Nitrate) is secondary pollutants formed as photochemical smog by interaction of oxides of nitrogen on hydrocarbons.

Answer: Option D. -> methyl isocyanate
:
D

Methyl isocyanate was the principle toxic gas responsible for Bhopal tragedy.

Answer: Option C. -> Reduction in the thickness of ozone layer in stratosphere            
:
C
It refers to reduction in the thickness of ozone layer. As ozone layer exists in stratosphere, option (c) is the correct answer.

Answer: Option D. -> Rain having pH value less than 7 is known as acid rain.
:
D
a) The lowest region of atmosphere is known as troposphere and above this region lies the stratosphere.
b) CO gas combines with hemoglobin present in blood to form carboxyhaemoglobin which is about 300 times more stable than oxyhaemoglobin. It reduces the oxygen carrying capacity of blood.
c) Atmospheric gases which are transparent to sunlight but not to heat radiation from earth surface are known as greenhouse gas. Water vapor acts as greenhouse gas. Hence
d) Rain having pH value less than 5.6 is termed as acid rain.