JEE Mains · Chemistry · STD 11 -p-Block elements - I

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 \(1350^{\circ} C\), while above \(1350^{\circ} C\) 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 \(A\).
C \(A\) is correct \(R\) is not correct.
D \(A\) is not correct. \(R\) is correct.

Verified Solution

Answer & Solution

Correct Answer

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

Step-by-step Solution

Detailed explanation

From Ellingham diagram given in NCERT, it can be seen that \(Mg , MgO\) line crosses \(Al , Al _{2} O _{3}\) line after \(1350^{\circ} C\) hence assertion is true. Yes, Mg have lower MP and BP than aluminium but it does not explain the above fact.

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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