The poisonous gas that is released during the combustion of petrol in a car engine is

Which of the following metal pollutants is present in the exhaust fumes of vehicles?

How is chemistry related to the environment? Describe it.

$A$ water sample has $ppm$ level concentration of the following metals: $Fe = 0.2$,$Mn = 0.05$,$Cu = 3.0$,$Zn = 5.0$. The metal that makes the water sample unsuitable for drinking is

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 $Y$.

$A$ large number of fish are suddenly found floating dead on a lake. There is no evidence of toxic dumping,but you find an abundance of phytoplankton. Suggest a reason for the fish kill.