<prompt> Hardness of water is expressed per litre m EqL, one unit which is equivalent to which one of the following.20 mg CaCO3 20 ppm30 mg CaCO3 30 ppm40 mg CaCO3 40 ppm50 mg CaCO3 50 ppm  <response>: Hardness of waterHardness of water is defined as the soap-destroying power of water.Water is considered to be bard if large amounts of soap are required to produce lather.The hardness is caused by high mineral content, Mainly calcium and magnesium cations.Hardness may be : -i Temporary Carbonate hardness Calcium bicarbonate Magnesium bicarbonate.It is called temporary because it can be removed by boiling or addition of lime.ii Permanent Non-Carbonate hardness Calcium Sulfate, magnesium sulfate, Calcium chloride, magnesium chloride.It is called permanent because it cannot be removed by boiling.Hardness is expressed in terms of mili-equilents per litre mEqL.One mEqL of hardness - producing ion is equal to 50 mg CaCO3 50ppm in one litre of water. 