An ideal gas expands from initial volume $5\ \text{dm}^3$ to $15\ \text{dm}^3$ against a constant external pressure of $2$ atm. What is the work done by the gas ?

A weak base is $1.3\%$ dissociated in its aqueous solution. If $K_b$ for weak base is $1.69 \times 10^{-5}$ at $298$ K. Find the concentration of aqueous solution of weak base.

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.
$3\text{H}_3\text{AsO}_{3(aq)} + \text{BrO}_{3(aq)}^- \longrightarrow \text{Br}_{(aq)}^- + 3\text{H}_3\text{AsO}_{4(aq)}$