The heat of combustion of carbon to CO2 is 393.5 kJ/mol. The heat released upon formation of 35.2g of CO2 from carbon and oxygen gas is:

The correct option is -315kJ
The molar mass of CO2 is 44 g/mol.
Number of moles of CO2 = (mass of CO2) / (molar mass of CO2) = 35.2 g / 44 g/mol = 0.8 mol
Heat released = number of moles × heat of combustion = 0.8 mol × 393.5 kJ/mol = 314.8 kJ ≈ 315 kJ
Since heat is released, the sign is negative. Therefore, the heat released is -315 kJ.