In a chemical equation, which symbol should be used to indicate that a substance is in solution?
(s)
(g)

(ag)

 In a chemical equation, (aq) should be used to indicate that a substance is in solution.

Explanation:

The chemical reaction is represented by putting the reactants at left side of the arrow and products on the right side of the arrow.  The salts which are soluble in water are designated by symbol (aq) and those which are insoluble in water and remain in solid form are represented by (s) after their chemical formulas.

The liquids are designated  by symbol (l) and gases are designated  by symbol (g).

In a chemical equation, (aq) should be used to indicate that a substance is in solution.