The correct answer is - hard water reacts to form the calcium or magnesium salt of the organic acid of the soap.
Explanation:
Soaps are made up of fatty acids or oils by treating with strong alkali and are salts of sodium and potassium. Hard water, on the other hand, has a high concentration of minerals in comparison to soft water. When hard water and soap are mixed together the salts of the minerals like Ca2+ and Mg2+ ions present in hard water react with fatty acids of the soap.
The sodium salts are changed to the salts of calcium and magnesium which are precipitated to an insoluble substance. The insoluble salts of the calcium or magnesium dirt stick on the clothes thus cleaning ability of soap is reduced.
For a 1st order reaction: In(n/n0)= -k * (time difference) so k= - In (n/n0)/ (t/t0) n is concentration at time t and n0 is the concentration at an earlier time t0. where k is constant.
The physical process of evaporation involves the heat absorbing and the status of the substance changing. The status of this substance changes form liquid to gas.