Question

Complete the following reaction that aids in the formation of acid rain.
+ [O] + H2O→H2SO4

• A. ${\mathrm{NO}}_2$
• B. ${\mathrm{SO}}_3$
• C. ${\mathrm{SO}}_2$

Answer 1

The correct option is C ${\mathrm{SO}}_2$

While burning sulphur containing fossil fuels, sulphur dioxide is released. This reacts with water vapours and form sulphurous acid.
$S\left(s\right)+O_2\left(g\right)\to {\mathrm{SO}}_2\left(g\right)$
${\mathrm{SO}}_2\left(g\right)+H_{2}O\left(l\right)\to H_2{\mathrm{SO}}_3\left(\mathrm{aq}\right)$
Substances in the upper atmosphere then catalyse the reaction between sulphurous acid and oxygen to form sulphuric acid.
$2H_2{\mathrm{SO}}_3\left(\mathrm{aq}\right)+O_2\left(g\right)\to 2H_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)$
This sulphuric acid reduces the pH of rainwater to nearly 5.6, which we call as acid rain.