Final answer:
The equation that represents a reversible reaction is c) P ↔ Q, with the double arrow indicating the reversibility of the reaction.
Step-by-step explanation:
The formula equation that shows a reversible reaction is c) P ↔ Q. A reversible reaction is one where the reactants can convert to products and the products can also revert back to reactants under certain conditions. This is indicated by the double arrow (↔) in the chemical equation. In the context of reversible reactions and equilibrium, several concepts are important, such as the reaction quotient (Q), equilibrium constant (Kc), and the direction in which the reaction will proceed to achieve equilibrium.
An example of a reversible reaction is CO(g) + H₂O(g) ↔ CO₂(g) + H₂(g). Here, carbon monoxide and water vapor can react to form carbon dioxide and hydrogen gas, and vice versa. The status of this reaction at equilibrium can be predicted by comparing the reaction quotient Q to the equilibrium constant Kc.