Given are two statements one is labelled as Assertion and other is labelled as Reason.
Assertion: Magnesium can reduce $$Al_2O_3$$ at a temperature below $$1350°$$C, while above $$1350°$$C aluminium can reduce MgO.
Reason: The melting and boiling points of magnesium are lower than those of aluminium.

We need to evaluate both the Assertion and Reason about the reduction of metal oxides.

Assertion: Magnesium can reduce $$Al_2O_3$$ at a temperature below $$1350°C$$, while above $$1350°C$$ aluminium can reduce MgO.

Analysis of Assertion:

This can be understood from the Ellingham diagram. At temperatures below about $$1350°C$$, the line for MgO formation lies below the $$Al_2O_3$$ line, meaning Mg has a more negative $$\Delta G$$ for oxide formation, so Mg can reduce $$Al_2O_3$$.

Above $$1350°C$$, the $$Al_2O_3$$ line crosses below the MgO line (because Mg boils around $$1090°C$$ and its oxide becomes less stable at higher temperatures). This means Al can now reduce MgO.

The Assertion is correct.

Reason: The melting and boiling points of magnesium are lower than those of aluminium.

Analysis of Reason:

Magnesium: Melting point = $$650°C$$, Boiling point = $$1090°C$$

Aluminium: Melting point = $$660°C$$, Boiling point = $$2519°C$$

Indeed, the melting and boiling points of Mg are lower than those of Al. The Reason is correct.

Is the Reason the correct explanation of the Assertion?

The crossover in the Ellingham diagram at $$1350°C$$ is primarily due to the increase in entropy when Mg boils (at $$1090°C$$), which makes the $$\Delta G$$ for MgO formation less negative. However, the Reason only states that Mg has lower melting and boiling points than Al — while this is related, it does not directly explain the thermodynamic crossover in the Ellingham diagram. The actual explanation involves the change in slope of the $$\Delta G$$ vs $$T$$ line due to the phase transition (boiling) of Mg.

Therefore, both statements are correct, but the Reason is not the correct explanation of the Assertion.

Hence, the correct answer is Option B: Both Assertion and Reason are correct, but Reason is NOT the correct explanation of Assertion.