Using very little soap while washing clothes, does not serve the purpose of cleaning of clothes, because

This question asks why using very little soap is ineffective for cleaning clothes.

Soap molecules are amphiphilic — they have a hydrophobic (non-polar) tail and a hydrophilic (polar) head. For effective cleaning, they must form micelles — spherical aggregates where the hydrophobic tails point inward (trapping grease) and the hydrophilic heads face outward (toward water). However, micelles form only when the concentration of soap in water exceeds a certain threshold called the Critical Micelle Concentration (CMC); below this concentration, soap molecules remain as individual ions or molecules and cannot aggregate into micelles.

When very little soap is used, the soap concentration in water remains below the CMC, preventing micelle formation and thus rendering the soap unable to effectively trap and remove grease and dirt from clothes.

Option A: Soap particles remain floating in water as ions — this is partially true but does not explain why cleaning fails.
Option B: Colloidal structure of soap in water is completely disturbed — incorrect, as the colloidal structure (micelles) was never formed in the first place.
Option C: The hydrophobic part of soap is not able to take away grease — incorrect reasoning; the hydrophobic part can still interact with grease, but without micelle formation, it cannot be effectively removed.
Option D: The micelles are not formed due to concentration of soap below its CMC value — this is the precise scientific explanation.

The correct answer is Option D: The micelles are not formed due to concentration of soap below its CMC value.