The dibromo compound [P] (molecular formula : C_ 9 H_ 10 Br_ 2 )...

The dibromo compound $[\mathrm{P}]$ (molecular formula : $\mathrm{C}_{9} \mathrm{H}_{10} \mathrm{Br}_{2}$) when heated with excess sodamide followed by treatment with dilute HCl gives $[\mathrm{Q}]$. On warming $[\mathrm{Q}]$ with mercuric sulphate and dilute sulphuric acid yield $[R]$ which gives positive lodoform test but negative Tollen's test. The compound $[\mathrm{P}]$ is :