Soaps

Step 1: Definition.
Soap is the sodium or potassium salt of long-chain fatty acids (such as stearic, palmitic, or oleic acid).
General formula: C H COONa (sodium stearate).
Step 2: Mechanism of cleansing.
Soap molecules have two parts:
- A long non-polar hydrocarbon tail (hydrophobic) that repels water but attracts grease/oil.
- A polar carboxylate head (hydrophilic) that is attracted to water.
Step 3: Action.
When soap is added to water containing dirt or grease:
- The hydrophobic tail dissolves in grease.
- The hydrophilic head faces the water.
This forms spherical aggregates called micelles, which trap the oily dirt inside and wash away with water.
Step 4: Equation.

Step 1: Recall soap definition.
Soaps are sodium or potassium salts of long-chain fatty acids.
Step 2: Check options.
- (A) C H COONa: Sodium stearate, a typical soap.
- (B) (C H COO) Ca: Insoluble salt (scum in hard water), not a soap.
- (C) C H COOH: Stearic acid, not soap.
- (D) C H COOH: Palmitic acid, also not soap.
Step 3: Conclusion.
Thus, the correct soap is C H COONa}.