Stearic acid and polyethylene glycol react to form which one of the following soap/detergents?

We need to identify the type of soap/detergent formed when stearic acid reacts with polyethylene glycol.

Detergents are classified into three types based on the nature of their hydrophilic head: (i) anionic detergents carry a negative charge, for example sodium alkyl sulphates and sodium alkylbenzene sulphonates; (ii) cationic detergents carry a positive charge, such as quaternary ammonium salts like cetyltrimethylammonium bromide; and (iii) non-ionic detergents have a hydrophilic part with no charge and are formed by the reaction of a long-chain fatty acid with polyethylene glycol.

Stearic acid $$CH_3(CH_2)_{16}COOH$$ is a long-chain fatty acid, and when it reacts with polyethylene glycol $$HO(CH_2CH_2O)_nH$$ it forms an ester:

This product has a long hydrocarbon chain serving as the hydrophobic tail from stearic acid, and a polyethylene glycol chain serving as the hydrophilic head which is polar due to multiple ether linkages but carries no ionic charge.

Since the hydrophilic part does not carry any charge (neither positive nor negative), this is a non-ionic detergent.

The product formed is a non-ionic detergent; it is not a soap, which requires a metal salt of a fatty acid, nor is it anionic or cationic.

Hence, the correct answer is Option D: Non-ionic detergent.