The concentration of dissolved oxygen $(DO)$ in cold water can go up to ......... $ppm$.

How is ozone formed in photochemical smog?

Which of the following causes "blue baby syndrome"?

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 acceptable level of carbon monoxide gas $(CO)$ in the atmosphere in $ppm$ level is

From where are the biodegradable wastes generated?