Question

Soap helps is cleaning clothes, because
(A) It attracts the dirt particles
(B) It decreases the surface tension of water
(C) It increases the cohesive force between water molecules
(D) It increases the angle of contact

Answer 1

Hint We understand the definition of soap here so we discuss the reason for using soap accordingly. A soap molecule consists of a chain of carbon atoms where oil is drawn from one end of the chain and water is drawn from the other. Soap should be balanced and the surface tension level should not be applied to too much or too little of the cleaning ingredient here.
Useful formula:
Surface tension of water,
\[F{\text{ }} = {\text{ }}2\gamma L{\text{ }} = {\text{ }}2\gamma 2\pi r{\text{ }} = {\text{ }}4\gamma \pi r\]
Where,
$F$ force applied
$r$ pressure inside a soap bubble
\[\gamma \] surface tension for soapy water

Complete step by step answer
Given by,
Soap helps is cleaning clothes
We find the reason,
The most popular substance used for cleaning is soap. The soap comes from saponification, a chemical process. The soap has a compound that is hydrophilic and hydrophobic. By decreasing surface tension, this dual quality helps to reduce soil.
As the soap is rubbed on a dirty fabric, the soap's hydrophobic molecule holds the dirt molecule on the cloth and the water holds the hydrophilic molecule.
The hydrophobic molecule draws out the dirt while rubbing and forms a micelle. The micelle is a soap-compound shell with dirt at its core. The hydrophilic molecules in the micelle's outer layer are mostly present.
The hydrophilic molecules in the micelle retain water and drag the dirt out when the fabric dips in the water. As all the soap compounds are from fats and oils, this reduces the surface tension in this process.
Hence, Soaps minimize water's surface tension in order to improve water's wetting capacity, which helps clean clothes.

Thus, option B is the correct answer

Note According to that, the addition of detergent to water decreases its friction on the surface. Detergents and soaps have something called a surface-active agent or for short, a surfactant. These surfactants decrease water's surface tension value and increase its ability to stick to things.