A 822-G Sample of Solid Calcium Reacted in Excess Fluorine Gas

A 8.22-g sample of solid calcium reacted in excess fluorine gas to give a 16-g sample of pure solid CaF₂.The heat given off in this reaction was 251 kJ at constant pressure.Given this information,what is the enthalpy of formation of CaF₂(s) ?

A) 251 kJ/mol
B) 250 kJ/mol
C) -1.23 × 10³ kJ/mol
D) -613 kJ/mol
E) 1.23 × 10³ kJ/mol