The entropy change can be calculated by using the expression $△\mathrm{S}=\frac{{\mathrm{q}}_{\mathrm{rev}}}{\mathrm{T}}$. When water freezes in a glass beaker, choose the correct statement amongst the following:           
 

$\mathrm{C} \left(\mathrm{graphite}\right) + \frac{1}{2}{\mathrm{O}}_2 \left(\mathrm{g}\right) \to \mathrm{CO} \left(\mathrm{g}\right) ; {∆}_{\mathrm{r}}\mathrm{H} = \mathrm{y} \mathrm{kJ} {\mathrm{mol}}^{-1}$

Consider the reactions given below. On the basis of these reactions find out which of the algebraic relations given in options (i) to (iv) is correct?

(a)$\mathrm{C} \left(\mathrm{g}\right) + 4\mathrm{H} \left(\mathrm{g}\right) \to {\mathrm{CH}}_4 \left(\mathrm{g}\right); {∆}_{\mathrm{r}}\mathrm{H} = \mathrm{x} \mathrm{kJ} {\mathrm{mol}}^{-1}$ 

(b) $\mathrm{C} \left(\mathrm{graphite},\mathrm{s} \right)+ 2{\mathrm{H}}_2 \left(\mathrm{g}\right) \to {\mathrm{CH}}_4 \left(\mathrm{g}\right); {∆}_{\mathrm{r}}\mathrm{H} = \mathrm{y} \mathrm{kJ} {\mathrm{mol}}^{-1}$