The correct option is B Boiling
In this method the calcium and magnesium bicarbonate present in water and decomposed into calcium and magnesium carbonates, which are insoluble in water, hence they settle down and soft water is drained. Ca(HCo3)2→CaCO3↓+Co2+H2oMg(HCo3)2→MgCO3↓+Co2+H2o