What indicates a system is in a state of chemical equilibrium?

A system is in a state of chemical equilibrium when there is a constant ratio of reactants and products present in the system. This occurs when the forward reaction (conversion of reactants to products) and the reverse reaction (conversion of products back to reactants) occur at the same rate. As a result, the concentrations of the reactants and products remain constant over time, even though they are still continually converting into one another.

In this scenario, the balance between the two reactions means that the overall concentrations stabilize, demonstrating that the system has reached equilibrium. It's important to note that this does not imply that the reactants have been completely consumed or that no reactions are occurring. Instead, it highlights the dynamic nature of the equilibrium state where both products and reactants coexist at specific concentrations.

Therefore, selecting the option that indicates a constant ratio of reactants and products as the sign of chemical equilibrium accurately reflects the fundamental principle of equilibrium in chemistry.