Hardness of water is expressed in equivalents of
CaCO3CaCO_3CaCO3
MgCO3MgCO_3MgCO3
Ca(HCO3)2Ca(HCO_3)_2Ca(HCO3)2
Mg(HCO3)2Mg(HCO_3)_2Mg(HCO3)2
(A) CaCO3CaCO_3CaCO3
Explanation: