Nowadays, tetrachloroethene $\left({\mathrm{Cl}}_2\mathrm{C}={\mathrm{CCl}}_2\right)$ solvent has been replaced by liquified ${\mathrm{CO}}_2$ for the dry cleaning purposes. This is because:

$\mathrm{X}$ is a hydrocarbon, $\mathrm{A}$ and $\mathrm{B}$ are neutral oxides of nitrogen, $\mathrm{C}$ is blue coloured gas and $\mathrm{D}$ is released when ${\mathrm{H}}_2\mathrm{S}$ is reacted with oxygen.

Identify the correct statements about $\mathrm{X}, \mathrm{A}, \mathrm{B}, \mathrm{C}$ and $\mathrm{D}$, which cause global warming.

$\mathrm{i}.$ $\mathrm{X}$ mainly present in natural gas.
$\mathrm{ii}.$ $\mathrm{A}$ combines with oxygen to produce $\text{'}\mathrm{B}\text{'}$.
$\mathrm{iii}.$ $\mathrm{C}$ is a main constituent of photochemical smog.
$\mathrm{iv}.$ $\mathrm{D}$ causes acid rain.

The anion/anions that make/makes the water sample unsuitable for drinking, in which ppm level concentration of  ${\mathrm{F}}^{-}=10, {\mathrm{SO}}_4^{2-}=100, {\mathrm{NO}}_3^{-}=50$  is/ are:

Suppose it rains during a thunderstorm. The collected rainwater has a $\mathrm{pH}$ value