Given are two statements one is labelled as Assertion A and other is labelled as Reason R. Assertion A: Magnesium can reduce $\mathrm{Al}_{2}\mathrm{O}_{3}$ at a temperature below $1350^{\circ}\mathrm{C}$, while above $1350^{\circ}\mathrm{C}$ aluminium can reduce MgO. Reason R: The melting and boiling points of magnesium are lower than those of aluminium. In light of the above statements, choose most appropriate answer from the options given below:

(B) Both A and R are correct, but R is NOT the correct explanation of A.

(A) Both A and R are correct, and R is correct explanation of A.

(C) A is correct R is not correct.

(D) A is not correct, R is correct.

General Principles and Processes of Isolation of Metals — JEE Main · 2022 · 28 Jun 2022 · Shift 1 Question with Solution

Given are two statements one is labelled as Assertion A and other is labelled as Reason R.
Assertion A: Magnesium can reduce

Al_{2} O_{3}

at a temperature below

135 0^{\circ} C

, while above

135 0^{\circ} C

aluminium can reduce MgO.
Reason R: The melting and boiling points of magnesium are lower than those of aluminium.
In light of the above statements, choose most appropriate answer from the options given below:

(A)Both A and R are correct, and R is correct explanation of A.
(B)Both A and R are correct, but R is NOT the correct explanation of A.✓ Correct
(C)A is correct R is not correct.
(D)A is not correct, R is correct.

Answer: (B)

Solution

Assertion A is correct: From the Ellingham diagram, the

Mg / MgO

line crosses the

Al / Al_{2} O_{3}

line at approximately

135 0^{\circ} C

. Below this temperature,

Δ G

for Mg oxidation is more negative than for Al, so Mg can reduce

Al_{2} O_{3}

. Above

135 0^{\circ} C

, the reverse is true, and Al can reduce MgO.

Reason R is also correct: Mg has lower melting and boiling points than Al (Mg: 650°C, 1090°C; Al: 660°C, 2470°C).

However, R does NOT explain A. The temperature-dependent reducing ability is governed by thermodynamic stability (Gibbs free energy changes in the Ellingham diagram), not by the physical properties (melting/boiling points) of the metals.

JEE Main · 2022 · 28 Jun 2022 · Shift 1 · Single correct option

JEE Main · 2022 · 28 Jun 2022 · Shift 1 · General Principles and Processes of Isolation of Metals

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