Permanent hardness due to `Mg^(2+)` ions is best removed by

Options

A. `Ca(OH)_(2)`
B. `Na_(2)CO_(3)`
C. `Na_(2)CO_(3)+Ca(OH)_(2)`
D. None of these

Answer

C

Explanation

`Ca(OH)_(2)` removes the permanent hardness due to `Mg^(2+)` ion, but it produces `Ca^(2+)` ions which are removed by `Na_(2)CO_(3)`.
`Ca^(2+)+Ca(OH)_(2)rarr Mg(OH)_(2)darr+Ca^(2+)`
`Ca(OH)_(2)+Na_(2)CO_(3) rarr CaCO_(3)darr + 2 Na ^(+)`
`Ca(OH)_(2) Na_(2)CO_(3)` alone cannot remove the permanent hardness.