2 . 4g coal is burnt in a bomb calorimeter in excess of oxygen at...

$C\left(s\right) + {O}_{2}\left(g\right) \to {CO}_{2}\left(g\right); \Delta H = - xkJ / mole$

$Q = C \Delta T = 20kJ \times 2$

$40kJ$ heat is released for $2 . 4g$ of $Carbon$

For $1$ mole '$Carbon$' $Q = \dfrac{40}{2 . 4} \times 12$

$= \dfrac{400}{24} \times 12 = 200kJ / mole$

$Q = \Delta E = \Delta H = 200kJ\left(∵ {\Delta n}_{g} = 0\right)$

$x = 200$