The compound X is ${\mathrm{KMnO}}_4$. It gives on heating the oxygen and ${\mathrm{K}}_2{\mathrm{MnO}}_4$ and ${\mathrm{MnO}}_2$. ${\mathrm{MnO}}_2$ formed the ${\mathrm{K}}_2{\mathrm{MnO}}_4$ on reaction with potassium hydroxide in presence of the potassium nitrate.

${\mathrm{KMnO}}_4\left(\mathrm{X}\right) \stackrel{\mathrm{Heating}}{\to } {\mathrm{K}}_2{\mathrm{MnO}}_4\left(\mathrm{Y}\right)+{\mathrm{MnO}}_2\left(\mathrm{Z}\right) +{\mathrm{O}}_2$

${\mathrm{MnO}}_2\left(\mathrm{Z}\right) +\mathrm{KOH}/{\mathrm{KNO}}_3\to {\mathrm{K}}_2{\mathrm{MnO}}_4\left(\mathrm{Y}\right)$

Hence, the compounds $\mathrm{X},\mathrm{Y}$ and $\mathrm{Z}$ respectively are $\mathrm{X}-{\mathrm{KMnO}}_4\mathrm{Y}-{\mathrm{K}}_2{\mathrm{MnO}}_4\mathrm{Z}-{\mathrm{MnO}}_2$.