A reddish-brown metal ‘M’ forms two oxides like MO and $M_{2}O$  which are present in black and Red color.

$2M+O_2\to \underset{\left(Black\right)}{MO};\mathrm{Pr}ocess\text{'}X\text{'}$

$4M+O_2\to \underset{\left(\mathrm{Re}d\right)}{2M_{2}O};\mathrm{Pr}ocess\text{'}Y\text{'}$

and sometimes the above-formed two oxides can be interconverted to one another as given below.

$\underset{\left(Black\right)}{MO}\underset{processZ}{\overset{processW}{\rightleftharpoons }}\underset{\left(\mathrm{Re}d\right)}{M_{2}O}$

Then identify the process W, X, Y, and Z respectively.