Which from following gases is adsorbed to greater extent if adsorbent remains same at similar conditions of temperature and pressure?

Which of the following is effectively used to remove E. coli bacteria from water?

What is order and molecularity of following reaction?

$$ \mathrm{NO}_{2(\mathrm{~g})}+\mathrm{NO}_{2(\mathrm{~g})} \longrightarrow 2 \mathrm{NO}_{(\mathrm{g})}+\mathrm{O}_{2(\mathrm{~g})} $$

The solubility of salt $\mathrm{BA}_2$ is $4 \times 10^{-4} \mathrm{~mol} \mathrm{dm}^{-3}$.

What is solubility product of the salt?