The correct option is A 9.38 g
2NaHCO3Heat−−−→Na2CO3+H2O+CO2↑
The molar mass of NaHCO3 is 84 g/mol.
The molar masses of CO2 and water are 44 g/mol and 18 g/mol respectively.
Thus, 2×84=168 g of NaHCO3 on decomposition will loose 44+18=62 g.
Hence, 1.68 g of NaHCO3 on decomposition will lose 0.62 g.
Hence, the weight of the residue will be 10−0.62=9.38 g.