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For a reaction, 4M(s) + nO2(g) → 2M2On(s), the free energy change is plotted as a function of temperature. The temperature below which the oxide is stable could be inferred from the plot as the point at which: (1) the slope changes from positive to zero (2) the free energy change shows a change from negative to positive value (3) the slope changes from negative to positive (4) the slope changes from positive to negative

1. the slope changes from positive to zero
2. the free energy change shows a change from negative to positive value
3. the slope changes from negative to positive
4. the slope changes from positive to negative

Correct answer: the slope changes from negative to positive

Solution

The correct option indicates that as the temperature increases, the free energy change transitions from being favorable (negative) to unfavorable (positive), suggesting that the oxide becomes unstable above this temperature, thus identifying the stability limit.

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