20 grams of metal carbonate on calcination gives 11.2 grams of metal oxide. Atomic weight of the bivalent metal is

Wmetal carbonateWmetal oxide=Emetal carbonateEmetal oxide; Wmetal carbonateWmetal oxide=EM+EcarbonateEM+Eoxide;                    2011.2=E+30E+8;                           E=20;                        AW=EW×Valency;                        AW=20×2=40;