Elements $X$ and $Y$ are both in period three. If the chloride of $X$ is put into water, it reacts and produces a solution of $\text{pH }2$. If the chloride of $Y$ is put into water, it dissolves and produces a solution of $\text{pH }7$. Which statement accounts for these observations?
- ABoth chlorides hydrolyse in water.
- B$X$ is phosphorus and $Y$ is aluminium.
- C$X$ is silicon and $Y$ is sodium.
- D$X$ is sodium and $Y$ is phosphorus.