JEE Main · 2023 · 29 Jan 2023 · Shift 1 · Hydrocarbons

The amount of hydrocarbon is $\frac{17\times 10^{-3}}{136}=1.25\times 10^{-4}\mathrm{mol}$, taking the molar mass of ${\mathrm{C}}_{10}{\mathrm{H}}_{16}$ as $136\mathrm{g}\mathrm{mo}{\mathrm{l}}^{-1}$. The hydrogen absorbed, measured at $0^{\circ }\mathrm{C}$ and $760\mathrm{mm}$, is $\frac{1\times (8.40/1000)}{0.0821\times 273}=3.75\times 10^{-4}\mathrm{mol}$. Each carbon--carbon double bond takes up one molecule of hydrogen, so the number of double bonds is the mole ratio $\frac{3.75\times 10^{-4}}{1.25\times 10^{-4}}=3$. The hydrocarbon holds three double bonds.