Which of the following pair of ions makes the water hard ?

Options

A. `Na^(+),SO_(4)^(2-)`
B. `Ca^(2+),HCO_(3)^(-)`
C. `Ca^(2+),NO_(3)^(-)`
D. `NH_(4)^(+),Cl^(-)`

Answer

b

Explanation

`HCO_(3) ^(-)` is main reason of temporary hardness of water.