Leakage of which gas was responsible for the Bhopal tragedy in $1984$?

The decomposition of organic compounds in the presence of oxygen and without the formation of odoriferous substances is called:

Which gas contributes the least to global warming?

Some reactions of $NO_2$ relevant to photochemical smog formation are:
$NO_{2(g)} \xrightarrow{hv} NO_{(g)} + X$
$X + O_2 \rightarrow Y$
$NO + Y \rightarrow NO_2 + A$
$O + O_2 + M \rightarrow B + M$
Identify $A, B, X$ and $Y$.

The effect of smog is observed on which of the following?

If the $pH$ of water increases above ......,the effectiveness of chlorination in water is reduced.