The correct option is C It removes Ca2+ and Mg2+ ions from water that causes hardness
Phosphates perform many functions in washing powders and detergent. They soften hard water by binding with calcium ions and magnesium ions. In this way, they prevent the lime in water from depositing or settling on the textile fibre. Phosphates counteract the effect of dissolved iron, calcium and magnesium ions that are present in hard water by preventing them from combining with other components of the formulation.