Let metal carbonate be : MCO3 and metal oxide is MO
MCO3⟶MO+CO2
1gm 0.56g
Number of equivalents of MCO3 is equal to the number of equivalents of MO.
So the oxide is CaO (M.wt. = 56) and metal carbonate is CaCO3 (M. wt = 100) metal is Ca (M.wt = 40). Eq wt. of metal ion is Ca2+ its eq. wt (402)=20g