Enthalpy of a compound is equal to its

The combustion enthalpies of carbon,hydrogen,and methane are $-393.5 \ kJ/mole$,$-284.8 \ kJ/mole$,and $-890.4 \ kJ/mole$ respectively at $25 \ ^oC$. The value of the standard formation enthalpy of methane at that temperature is ..... $kJ/mole$.

For the reactions $(i) \, H_{2(g)} + Cl_{2(g)} \to 2HCl_{(g)} + x \, kJ$ and $(ii) \, H_{2(g)} + Cl_{2(g)} \to 2HCl_{(\ell)} + y \, kJ$,which of the following statements is correct?

What is enthalpy of reaction?

The heat of formation is the change in enthalpy accompanying the formation of a substance from its elements at $298 \ K$ and $1 \ atm$ pressure. Since the enthalpies of elements are taken to be zero,the heat of formation $(\Delta H_f)$ of compounds

The heat of combustion of $C$,$S$ and $CS_2$ are $-393.3 \ kJ$,$-293.7 \ kJ$ and $-1108.76 \ kJ$ respectively. What will be the heat of formation of $CS_2$ in $kJ$?