$A$ water sample has $ppm$ level concentration of following anions:
$F^- = 10; \, SO_4^{2-} = 100; \, NO_3^- = 50$
The anion/anions that make/makes the water sample unsuitable for drinking is/are:

Excess of which of the following in water causes blue baby syndrome disease?

Explain the formation of photochemical smog with reactions.

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 $SO_2$

What is Biochemical Oxygen Demand $(BOD)$?

What is the percentage of oxygen by volume in dry air (in $\%$)?