The correct answer is (a) Cetyltrimethylammonium bromide
Explanation: Cetyltrimethylammonium bromide is a quaternary salt cation with bromine as the anion. The cationic part participates in the cleansing mechanism. Pentaerythritol monostearate is a non-ionic detergent, whereas sodium dodecyl sulphate and sodium lauryl sulphate are anionic detergents.