Mention the harmful effect of ultra violet radiations.

The chlorine free radical reacts with ozone to form a ..... free radical.

List gases which are responsible for the greenhouse effect.

The possibility of photochemical smog formation is more at

Identify the correct statements from the following:
$a$) $BOD$ value of clean water is less than $5 \ ppm$
$b$) Oxidation of ethene in the presence of $Pd^{2+}$ catalyst in aqueous medium gives acetic acid
$c$) Photochemical smog causes damage to plant life
$d$) Reducing smog is a mixture of smoke,fog and $SO_2$

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