Given: CaCO3→CaO+CO2
1 mole of CaO is produced by the decomposition of 1 mole of CaCO3
i.e. 56 g of CaO is produced by 10056×80=142.85 g of CaCO3
% purity=mass of pure compound in sampletotal mass of impure sample ×100=142.85200×100=71.43%
Hence, option (b) is correct.