Step 1: Understanding the Concept:
Cationic detergents have a positively charged head, usually a quaternary ammonium group, and a long hydrocarbon tail. They are mostly used as germicides and conditioners.
Step 2: Apply:
Hair conditioners contain cationic detergents such as cetyltrimethylammonium chloride. The positive head sticks to negatively charged hair and makes it smooth. Liquid detergent and household detergent use anionic ones (like sodium alkylbenzene sulphonate). Toothpaste uses mild anionic foaming agents such as sodium lauryl sulphate.
Step 3: Conclusion:
Option (A).
Final Answer:
Hair conditioner uses cationic detergent.
\[ \boxed{A:\ \text{Hair conditioner}} \]