Soaps are water soluble while detergents are water insoluble.

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Hint:Soaps are only soft water and on the other hand, detergents are soluble in both hard and soft water. Hard water contains salts or ions like calcium and magnesium in them and soft water is devoid of such ions.

Complete answer:
Soaps used for cleaning purposes are sodium or potassium salts of long chain fatty acids like stearic acid, oleic acid and palmitic acid. Soaps containing sodium salts are formed by heating fat or glycerol ester of fatty acid with aqueous sodium hydroxide solution. This reaction is known as saponification. Soaps are biodegradable. On the other hand, detergents are non biodegradable. Detergents are sodium or ammonium salt of higher sulphonic acid. Cleaning action of detergents is much more efficient and effective than that of soap. Soaps do not work in hard water but detergents can be used in both hard and soft water as well. This is because hard water contains calcium and magnesium ions. These ions form insoluble calcium and magnesium soaps respectively when sodium or potassium soaps are dissolved in hard water.
For example: \[2{{\text{C}}_{17}}{{\text{H}}_{35}}{\text{COONa}} + {\text{CaC}}{{\text{l}}_2} \to 2{\text{NaCl}} + {\left( {{{\text{C}}_{17}}{{\text{H}}_{35}}{\text{COO}}} \right)_2}{\text{Ca}}\] where \[{\left( {{{\text{C}}_{17}}{{\text{H}}_{35}}{\text{COO}}} \right)_2}{\text{Ca}}\] is insoluble calcium stearate. These insoluble soaps separate as scum in water and are useless as cleansing agents, in fact, these are a hindrance to good washing, mass. Hair washed with hard water looks dull because of this sticky precipitate. Dyes does not absorb evenly on cloth washed with soap using hard water, because of this gummy mass.

Thus, the correct option is B.

Detergents are similar to soaps but are more soluble in water, because the polar sulphonate of detergents is less likely than the polar carboxyl of soap to bind to calcium and other ions like magnesium found in hard water.