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

Option (d) is the correct answer.

Explanation:

When a substance is present in a solution then it is represented by a symbol "(aq)" which means aqueous.

When a substance is present in a solid state in a solution then it is indicated by a symbol "(s)" which means solid.

When a substance is present in a liquid state in a solution then it is indicated by a symbol "(l)" which means liquid.

When a substance is present in a gaseous state in a solution then it is indicated by a symbol "(g)" which means gas.

Hence, we can conclude that in a chemical equation, (aq) symbol should be used to indicate that a substance is in solution.

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.