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Question #44286

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The Question

Consider the elements $\ce{Li}$ , $\ce{Be}$ , $\ce{Mg}$ , and $\ce{Al}$ . The diagonal relationship between $\ce{Li}/\ce{Mg}$ and $\ce{Be}/\ce{Al}$ often leads to similarities in their ionic potentials ( $\phi$ ). However, successive ionization energies are strictly governed by the effective nuclear charge ( $Z_{eff}$ ) and the exact electronic configuration of the intermediate cations. Which of the following correctly represents the decreasing order of the second ionization energies ( $IE_2$ ) for these four elements?

Options

A.
$\ce{Li} > \ce{Al} > \ce{Be} > \ce{Mg}$
B.
$\ce{Li} > \ce{Be} > \ce{Al} > \ce{Mg}$
C.
$\ce{Li} > \ce{Be} > \ce{Mg} > \ce{Al}$
D.
$\ce{Be} > \ce{Li} > \ce{Al} > \ce{Mg}$

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Exception_Exposure

Learn to identify edge cases and boundary exceptions that JEE examiners hide in math problems.

Concepts Behind This Question

Effective Nuclear Charge (Zeff)|Successive Ionization Energies|Diagonal Relationship

Why This Question Is Tricky

Common Mistakes

This question tests the 'Hidden Variable' of intermediate cation electronic configurations overriding general periodic trends.

Students heavily rely on the heuristic that Period 2 elements always have higher ionization energies than their Period 3 counterparts (e.g., Be > Al).

The trap is failing to evaluate the specific state during the second ionization.

Because Al+ achieves a stable, fully filled 3s2 configuration while Be+ is left with a 2s1 configuration, the energy required to break the paired 3s2 state in Al+ exceeds the energy to remove the 2s1 electron in Be+, perfectly inverting the expected size-based heuristic.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Classification of Elements and Periodicity in Properties - Class 11 Part 1
Concept	Effective Nuclear Charge (Zeff)
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free