A sample of MgCO3 is 50 % pure. If on heating 4.0 g of MgO and 4.4 gm of CO2 are formed. Calculate amount of MgCO3 taken. [ Mg = 24, C = 12, O = 16]

MgCO3 = MgO + CO2

84g            40g     44g

                    4g       4.4g

100 g MgCO3 contains = 50 g MgCO3

84 g MgCO3 contains   = 42 g MgCO3

Now

40g MgO produced by = 42 g MgCO3

4 g MgO produced by =4.2 g MgCO3

so ,the amount of MgCO3 taken is 4.2 g