$\mathop {{C_6}{H_{10}}}\limits_{Cyclohexene} + {H_2} \to \mathop {{C_6}{H_{12}},}\limits_{Cyclohexane} \,\,\,\,\,\,\,\,\,\,\,\Delta {H_1} = ?.....(1)$
Let us write the given facts
${H_2} + \frac{1}{2}{O_2} \to {H_2}O;$
$\Delta {H_2} = - 241\,\,kJ/mol.....(2)$
${C_6}{H_{10}} + \frac{{17}}{2}{O_2} \to 6C{O_2} + 5{H_2}O,$
$\Delta {H_3} = - 3800\,kJ/mol.....(3)$
${C_6}{H_{12}} + 9{O_2} \to 6C{O_2} + 6{H_2}O,$
$\Delta {H_4} = - 3920\,kJ/mol.....(4)$
The required reaction $(1)$ can be obtained by adding equations $(2)$ and $(3)$, and subtracting $(4)$ from the sum of $(2)$ and $(3)$.
${C_6}{H_{10}} + {H_2} \to {C_6}{H_{12}}$
$\Delta {H_1} = (\Delta {H_2} + \Delta {H_3}) - \Delta {H_4}$
$ = [ - 241 + ( - 3800)] - ( - 3920)$
$ = ( - 241 - 3800) - ( - 3920)$
$ = - 4041 + 3920 = - 121\,kJ/mol$
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$(A)$ the reaction of $Al _2 O _3$ with coke ($C$) at a temperature $>2500^{\circ} C$.
$(B)$ the neutralization of aluminate solution by passing $CO _2$ gas to precipitate hydrated alumina $\left( Al _2 O _3 .3 H _2 O \right)$
$(C)$ the dissolution of $Al _2 O _3$ in hot aqueous $NaOH$.
$(D)$ the electrolysis of $Al _2 O _3$ mixed with $Na _3 AlF _6$ to give $Al$ and $CO _2$.
$\begin{array}{*{20}{c}}
{O = C - C{H_2} - CH - CHO} \\
{|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,|\,\,\,\,\,\,\,\,\,\,} \\
{OH\,\,\,\,\,\,H - C = O\,\,}
\end{array}$