Explanation:

The description provided, 'Sodium salts of sulphonic acids or ammonium salts with chlorides or bromides', accurately defines the chemical composition of synthetic detergents. Detergents are cleaning agents that are structurally similar to soaps but are derived from petrochemicals and are generally more effective in hard water. For example, sodium alkylbenzenesulfonates are common anionic detergents. Soaps (Option A) are typically sodium or potassium salts of long-chain fatty acids. Baking powder (Option C) is a dry chemical leavening agent, a mixture of a carbonate or bicarbonate and a weak acid. Baking soda (Option D) is sodium bicarbonate ($\text{NaHCO}_3$). Therefore, the given chemical description refers to detergents.