The gaseous substances produced when a mixture of $\text{Ca(OH)}_2$ and $\text{NH}_4\text{Cl}$ is heated are led over solid CaO. The CaO removes water vapour, and gas W is then collected. A sample of W is oxidised by $\text{Cl}_2(g)$, forming two gases, X and Y. X is an element. Y is acidic. Y reacts with W to form Z. Identify X and Z.
- AX: $\text{N}_2$, Z: $\text{CaCl}_2$
- BX: $\text{N}_2$, Z: $\text{NH}_4\text{Cl}$
- CX: $\text{O}_2$, Z: $\text{CaCl}_2$
- DX: $\text{O}_2$, Z: $\text{NH}_4\text{Cl}$