Chemistry · May / June 2026 · Paper 12 · Question 40

An unknown salt, X, contains only one cation and only one anion. Aqueous sodium hydroxide is added to an aqueous solution of X. A white precipitate is formed that is soluble in excess aqueous sodium hydroxide. Aluminium foil is then added to the mixture and the mixture is warmed. A gas is produced that turns damp red litmus paper blue. Which ions are in salt X?

1. ANH$_4^+$ and SO$_3^{2-}$
2. BAl$^{3+}$ and NO$_3^-$
3. CCa$^{2+}$ and NO$_3^-$
4. DZn$^{2+}$ and SO$_3^{2-}$

As printed in the paper