A certain metal salt solutions is electrolysed in series with a silver coulometer. The weights of silver and the metal deposited are 0.5094 g and 0.2653 g. Calculate the valency of the metal if its atomic weight is nearly that of silver.

When $\mathrm{ZnS}$ is boiled with strong nitric acid, the products are zinc nitrate, sulphuric acid and nitrogen dioxide. What are the changes in the oxidation numbers of $\mathrm{Zn},\mathrm{S}$ and $\mathrm{N}$:

${\mathrm{CN}}^{-}$ is oxidised by ${\mathrm{NO}}_3^{-}$ in the presence of an acid : ${\mathrm{aCN}}^{-}+{\mathrm{bNO}}_3^{-}+{\mathrm{cH}}^{+}⟶\left(\mathrm{a}+\mathrm{b}\right)\mathrm{NO}+{\mathrm{aCO}}_2+\frac{\mathrm{c}}{2}{\mathrm{H}}_2\mathrm{O}$. What are the whole number values of $\mathrm{a}, \mathrm{b}, \mathrm{c}$ in that order?

Which of the following solutions will exactly oxidize $25 \mathrm{mL}$ of an acid solution of $0.1 \mathrm{M}$ iron$\left(\mathrm{II}\right)$ oxalate?