What does the symbol (aq) represent in a chemical equation?

In a chemical equation, the reactant, or initial compound, is on the left side of the reaction, and the product, or final compound, is on the right side of the reaction.

Many symbols are used when expressing a chemical equation. Similar to this, various symbols, including those listed below, are employed to describe the physical state of the reacting entities during the course of the reaction.
For solid-state, use the symbol (s).
The liquid state is indicated by the symbol (l).
The gaseous state is represented by the symbol (g).
The aqueous solution is represented by the symbol (aq).
An aqueous solution (aq) denotes a substance that has been dissolved in water. The word aqueous is where the sign (aq) originates.
As a result, choice D is right.