100mL of a water sample contains 0.81g of calcium bicarbonate and 0.73 of magnesium bicarbonate. The hardness of this water sample expressed in terms of equivalents of CaCO 3​ is:(molar mass of calcium bicarbonate is 162g mol^−1 and magnesium bicarbonate is 146 gmol −1 )

(A) 1000 ppm

(B) 10000 ppm

(C) 100 ppm

(D) 5000 ppm

Solution :

neq​.CaCO3​=neq​Ca(HCO3​)2​+neq​Mg(HCO3​)2​

or 

(W​÷100) ×2 = (0.81​÷ 162)×2 + (0.73÷146)​×2 

∴w=1.0

∴ Hardness=(1.0÷100) ×10^6=10000ppm

Hence correct option is (B) 10000ppm