Compounds with high heat of formation are less stable because

Which among the following represents the reaction of formation of the product?

When $0.5 \ g$ of sulphur is burnt to $SO_2$,$4.6 \ kJ$ of heat is liberated. What is the enthalpy of formation of sulphur dioxide in $kJ \ mol^{-1}$?

The heat of neutralisation of one equivalent of an acid by one equivalent of a base is minimum when:

If $C_{(s)} + O_{2(g)} \rightarrow CO_{2(g)}$,$\Delta H = -X$,and $CO_{(g)} + \frac{1}{2} O_{2(g)} \rightarrow CO_{2(g)}$,$\Delta H = -Y$,calculate $\Delta_f H$ for $CO_{(g)}$ formation.

The heat of solution of anhydrous $CuSO_4$ and $CuSO_4 \cdot 5 H_2 O$ are $-70 \ kJ \ mol^{-1}$ and $+12 \ kJ \ mol^{-1}$ respectively. The heat of hydration of $CuSO_4$ to $CuSO_4 \cdot 5 H_2 O$ is $-x \ kJ$. The value of $x$ is: