Chlorine reacts with dilute hydrobromic acid to form _____ and bromine.

An element $\mathrm{X}$ forms two oxides $\mathrm{XO}$ and ${\mathrm{XO}}_2$. The oxide $\mathrm{XO}$ is neutral but ${\mathrm{XO}}_2$ is acidic in nature.The element $\mathrm{X}$ is most likely to be 

Four elements W, X, Y, and Z have atomic numbers 12,18, 4, and 16:

Which of the above will form an acidic oxide?