100 grams of metal carbonate on calcination gives 56 grams of metal oxide. Atomic weight of the bivalent metal is

Wmetal carbonateWmetal oxide=Emetal carbonateEmetal oxide; Wmetal carbonateWmetal oxide=EM+EcarbonateEM+Eoxide;                    10056=E+30E+8;                    44E=880;                          E=20;                      AW=EW×Valency;                      AW=20×2=40;