NaCl on dissociation gives Na+and Cl−ions as follows:
NaCl(aq)
Sodium‌chloride
→
Na+
Common‌ions
+Cl−(ions) While, soap in the solution gives RCOO−and Na+ions as follows: R−
CO‌
−
O
‌
+
Na
(s)
Soap
→RCOO−+Na+ ∴ Solubility of soap decrease due to common ion (Na+) present in the solution due to Le-Chatelier's principle, reaction shifts towards the reactant side.