What symbol is used to indicate a reversible reaction in chemical equations?

The symbol used to indicate a reversible reaction in chemical equations is the double-headed arrow, represented as ⇌. This notation signifies that the reaction can proceed in both the forward and reverse directions. In the context of a reversible reaction, the reactants can form products, and those products can also revert back to the original reactants. This is a crucial concept in chemistry because it highlights the dynamic nature of chemical processes, where equilibrium can be established between reactants and products.

The other symbols do not convey the same meaning: the single-headed arrow (→) indicates a one-way reaction, meaning reactants completely convert into products without reverting. The left arrow (←) typically represents the reverse process in a dual-procedure but does not signify a reversible reaction by itself. The symbol for not equal (≠) is irrelevant to chemical reactions and does not apply in this context. Thus, the double-headed arrow is the correct representation for reversible reactions.