In the given reaction

 $$\begin{gathered} {\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{CH}={\mathrm{CHCH}}_3\stackrel{\mathrm{x}}{⟶} \\ {\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{COOH}+{\mathrm{CH}}_3\mathrm{COOH} \end{gathered}$$
The X is 

A doubly bonded carbon atom having an alkyl group. is oxidised to aldehyde which is further oxidised to carboxylic acid.
$$\begin{gathered} {\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{CH}={\mathrm{CHCH}}_3\frac{\text{ (i) }{\mathrm{KMnO}}_4,{\mathrm{OH}}^{-}}{⟶} \\ \underset{\downarrow }{{\mathrm{CH}}_3\mathrm{CHO}} + \underset{\downarrow }{{\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{CHO}} \\ {\mathrm{CH}}_3\mathrm{COOH} {\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{COOH} \end{gathered}$$