An organic compound $\left(\mathrm{P}\right)$ with molecular formula ${\mathrm{C}}_5{\mathrm{H}}_8{\mathrm{O}}_4$ is stable to heat but hydrolyse to $\left(\mathrm{Q}\right)$ and $\mathrm{MeOH}$ by $\mathrm{NaOH}$ followed by acidification. $\left(\mathrm{Q}\right)$ on strong heating gives $\left(\mathrm{R}\right)$ which with red $\mathrm{P}/\mathrm{HI}$ gives ethane. The compound $\left(\mathrm{P}\right)$ is: