Water is said to be temporarily hard when it contains

A.

Ca (HCO3)2 and Mg (HCO3)2 salts

B.

Ca (HCO3)2 and CaCO3 SALTS

C.

Mg(HCO3)2 and CaSO4 salts

D.

CaSO4 and Ca(HCO3)2 salts

Correct answer is A

Temporary hardness is caused by the presence of dissolved calcium hydrogentrioxocarbonate(IV)  and magnesium hydrogentrioxocarbonate(IV) which decomposes on heating to form calcium trioxocarbonate(IV) and magnesium trioxocarbonate(IV) respectively.