$2{\mathrm{H}}_{2\left(\mathrm{ }\mathrm{g}\right)}+{\mathrm{O}}_{2\left(\mathrm{ }\mathrm{g}\right)}\to 2{\mathrm{H}}_2{\mathrm{O}}_{\left(l\right)};\Delta \mathrm{H}=-$ ve and $\Delta \mathrm{G}=$ $-$ ve. Then the reaction is

Balanced chemical reaction. 

$2{\mathrm{H}}_{2\left(\mathrm{ }\mathrm{g}\right)}+{\mathrm{O}}_{2\left(\mathrm{ }\mathrm{g}\right)}\to 2{\mathrm{H}}_2{\mathrm{O}}_{\left(l\right)}$

Change in Gibbs free energy equation.

$\Delta G=\Delta H-T\Delta S$

Where, $\Delta H$ is change in enthalpy and $∆\mathrm{S}$ is change in entropy.

$\Delta G=-ve$ for spontaneous

When we move gas to liquid $\Delta S$ decreases and reaction becomes spontaneous. When $\Delta H$ is negative system released heat and reaction become exothermic.

Therefore, option C is correct.