The gas known as a greenhouse gas is ...... .

Pollution can be controlled by

Observe the following statements:
Statement-$I$: The carbon-containing components of photochemical smog are acrolein,methanal,and $PAN$.
Statement-$II$: The number of greenhouse gases in the list given below is $5$: $CH_4, CO_2, NO, H_2O_{(l)}, H_2O_{(g)}, O_2, O_3$.
The correct answer is:

$A$ water sample is reported to be highly polluted if the $BOD$ (Biological Oxygen Demand) value of the sample becomes:

Identify $X$,$Y$,and $Z$ in the following reaction. (Equation not balanced)
$ClO + NO_2$ $\rightarrow \underline{X}$ $\xrightarrow{H_2O} \underline{Y} + \underline{Z}$

Explain in short: Pollution of the troposphere caused by hydrocarbons.