Which statement is true about a reaction that has a Kc value much greater than 1?

In a reaction where the equilibrium constant (Kc) value is much greater than 1, this indicates that at equilibrium, the concentration of products is significantly higher than that of reactants. This means that the forward reaction has produced a large amount of product compared to the starting materials.

Therefore, the statement suggesting that no reactants remain, indicating completion, aligns well with the implication of a high Kc value. When Kc is considerably greater than 1, it suggests that the reaction tends heavily toward the products side, indicating that the reactants are largely consumed in the process, reflecting a shift toward completion.

When analyzing the other statements, a reaction at equilibrium (with a Kc value much greater than 1) doesn’t necessarily mean there are no reactants left; rather, there may still be small amounts present. Additionally, while the system's stability can be inferred from this high value, a high Kc does not inherently indicate instability, and thus the system may still be stable as it has reached equilibrium. Therefore, the chosen statement accurately describes the situation presented by a Kc significantly larger than 1.