What is the pH of solution containing $5 \times 10^{-4}\ \text{M}\ \text{H}^+$ ion?

Identify change in oxidation state of oxidising agent in following redox reaction.
$3\text{H}_3\text{AsO}_{3(aq)} + \text{BrO}_{3(aq)}^- \longrightarrow \text{Br}_{(aq)}^- + 3\text{H}_3\text{AsO}_{4(aq)}$

Which element from following forms superoxide with oxygen?

What is the number of chiral carbon atoms in 2-chlorobutane?