Answer is :c) Gas(hydrogen sulfide)
N(Ca)/2 = n(O)/1 = n(CaO)/2
The calcium and the Calcium Oxide are divided by 2 because of their coefficients
there is no number in front of the oxygen so it is over one.
Hope this helped!!
since the unit for the heat of fusion is kJ/mol, you're going to have to convert the grams into moles in order to cancel out the unit. After that, you can solve like normal.