The standard enthalpy of combustion at 25 °C of ${\mathrm{H}}_2\left(\mathrm{g}\right)$ cyclohexene(g) and cyclohexane(g) are - 241, - 3800 and $-3920 \mathrm{kJ} {\mathrm{mol}}^{-1}$ respectively. The standard enthalpy of hydrogenation of cyclohexene will be

${\mathrm{C}}_6{\mathrm{H}}_{10}\left(\mathrm{g}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right)\to {\mathrm{C}}_6{\mathrm{H}}_{12}\left(\mathrm{g}\right)$

$\left(\mathrm{I}\right) {\mathrm{C}}_6{\mathrm{H}}_{12}\left(\mathrm{g}\right)+9{\mathrm{O}}_2\left(\mathrm{g}\right)\to 6{\mathrm{CO}}_2\left(\mathrm{g}\right)+6{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$

$\text{ (ii) }{\mathrm{C}}_6{\mathrm{H}}_{10}\left(\mathrm{g}\right)+\frac{17}{2}{\mathrm{O}}_2\left(\mathrm{g}\right)\to 6{\mathrm{CO}}_2\left(\mathrm{g}\right)+5{\mathrm{H}}_2\mathrm{O}\text{ (1) }$

$\text{ (iii) }{\mathrm{H}}_2\left(\mathrm{g}\right)+\frac{1}{2}{\mathrm{O}}_2\left(\mathrm{g}\right)\to {\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$

$$\begin{gathered} \mathrm{\Delta }H=\mathrm{\Delta }{H}_{\text{(ii) }}+\mathrm{\Delta }{H}_{\text{(iii) }}-\mathrm{\Delta }{H}_{\text{(i) }} \\ =[-3800-241-(-3920\left)\right]\mathrm{kJ}{\mathrm{mol}}^{-1} \\ =-121\mathrm{kJ}{\mathrm{mol}}^{-1} \end{gathered}$$

Thus the option C is correct.