Hydrocarbons

An alkene $X\left(\mathrm{C}_4 \mathrm{H}_8\right)$ exhibits geometrical isomerism. Oxidation of $A$ with $\mathrm{KMnO}_4 / \mathrm{H}^{+}$gave $Y$. On heating sodium salt of $Y$ with a mixture of NaOH and CaO gave $Z$. What is $Z$ ?