Balanced chemical equation for the above reaction is:-
CaCO3 -------> CaO + CO2
Atomic mass of Ca= 40 g/mol
Atomic mass of Carbon = 12g/mol
Atomic mass of oxygen = 16 g/mol
Molar mass of CaCO3 = 100 grams
Moles of CaCO3 heated = 25/100 =0.25
According to stoichieometry of the reaction:-
1 mole of CaCO3 prodecess 1 mole of CaO
Ratio of CaCO3 :CaO = 1:1
Hence 0.25 moles of CaCO3 producess 0.25 moles of CaO