AP EAMCET · Chemistry · Classification of Elements and Periodicity in Properties

The first ionization enthalpies of $Mg$ and $Al$ can be expected to be

A ${IE}_{1} (Mg) = 577.5 kJ \cdot {mol}^{- 1}, {IE}_{1} (A l) = 577.5 kJ . {mol}^{- 1}$
B ${IE}_{1} (Mg) = 577.5 kJ . {mol}^{- 1}, {IE}_{1} (A l) = 737.7 kJ . {mol}^{- 1}$
C ${IE}_{1} (Mg) = 737.7 kJ . {mol}^{- 1}, {IE}_{1} (A l) = 737.7 kJ . {mol}^{- 1}$
D ${IE}_{1} (Mg) = 737.7 kJ . {mol}^{- 1}, {IE}_{1} (Al) = 577.5 kJ . {mol}^{- 1}$

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Correct Answer

(D) ${IE}_{1} (Mg) = 737.7 kJ . {mol}^{- 1}, {IE}_{1} (Al) = 577.5 kJ . {mol}^{- 1}$

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Detailed explanation

Magnesium has the atomic number of 12. It has the electronic configuration of Ne3s2. It has the fully filled orbitals. So, it has the high ionisation energy. The atomic number of the aluminium is 13. It has the electronic configuration of Ne3s23p1. It has the low value of the…

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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The first ionization enthalpies of Mg and Al can be expected to be

Step-by-step Solution

The first ionization enthalpies of $Mg$ and $Al$ can be expected to be