Which of the following is not correct?

<p>The statement that is not correct among the given options is Option A.</p> <p>Option A states that $\Delta \mathrm{G}$ is positive for a spontaneous reaction, which is incorrect. The criterion for spontaneity in a chemical reaction is based on the Gibbs free energy change ($\Delta \mathrm{G}$) for the process. A spontaneous reaction is one that occurs without needing continuous input of energy from an external source. The correct relation is that for a spontaneous reaction, $\Delta \mathrm{G}$ is negative ($\Delta \mathrm{G} < 0$). When $\Delta \mathrm{G}$ is negative, it indicates that the process can occur spontaneously under the given conditions.</p> <p>Option B accurately states that $\Delta \mathrm{G}$ is positive for a non-spontaneous reaction. A positive value of $\Delta \mathrm{G}$ ($\Delta \mathrm{G} > 0$) indicates that the reaction is not spontaneous under the given conditions and requires external energy to proceed.</p> <p>Option C is correct in stating that $\Delta \mathrm{G}$ is zero for a reversible reaction at equilibrium. When a reaction is at equilibrium, it has reached a state where the forward and reverse reactions occur at equal rates, and there is no net change in the composition of the system. At this point, the Gibbs free energy is at its minimum for the given conditions, and $\Delta \mathrm{G} = 0$, indicating that the system is in a state of maximum stability and no further net change can occur without the input or removal of energy.</p> <p>Option D correctly states that $\Delta \mathrm{G}$ is negative for a spontaneous reaction. As explained previously, a negative Gibbs free energy change signifies that a process or reaction can proceed spontaneously in the direction written.</p>