Class NEET 2026 ALL Q #1988
COMPETENCY BASED
APPLY
4 Marks 2026 NTA-RE-NEET-2026 MCQ SINGLE
The highest occupied molecular orbital for $Ne_{2}$ is
(A) $\sigma_{2p}^{*}$
(B) $\pi_{2p}$
(C) $\sigma_{2p}$
(D) $\pi_{2p}$
Correct Answer: A

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Detailed Solution

Step 1: Determine Total Electrons

Neon (Ne) has an atomic number of 10. Therefore, the $Ne_{2}$ molecule contains a total of 20 electrons (10 + 10).

Step 2: Apply Molecular Orbital Theory (MOT) Configuration

For molecules with more than 14 electrons (like $O_{2}$ and $Ne_{2}$), the energy order of molecular orbitals is: $$\sigma_{1s} < \sigma_{1s}^{*} < \sigma_{2s} < \sigma_{2s}^{*} < \sigma_{2p_z} < \pi_{2p_x} = \pi_{2p_y} < \pi_{2p_x}^{*} = \pi_{2p_y}^{*} < \sigma_{2p_z}^{*}$$

Step 3: Fill the Orbitals

Distributing 20 electrons: $$\sigma_{1s}^2, \sigma_{1s}^{*2}, \sigma_{2s}^2, \sigma_{2s}^{*2}, \sigma_{2p_z}^2, \pi_{2p_x}^2, \pi_{2p_y}^2, \pi_{2p_x}^{*2}, \pi_{2p_y}^{*2}, \sigma_{2p_z}^{*2}$$

Step 4: Identify the Highest Occupied Molecular Orbital (HOMO)

The last electrons enter the $\sigma_{2p_z}^{*}$ orbital (often denoted as $\sigma_{2p}^{*}$). Thus, the HOMO is $\sigma_{2p}^{*}$.

Final Answer: A

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Pedagogical Audit
Bloom's Analysis: This is an APPLY question because the student must apply the principles of Molecular Orbital Theory to a specific diatomic system to determine electronic configuration.
Knowledge Dimension: CONCEPTUAL
Justification: The question tests the understanding of energy level ordering in homonuclear diatomic molecules, which is a core concept in Chemical Bonding.
Syllabus Audit: In the context of NEET, this is classified as COMPETENCY. It requires the student to differentiate between the energy ordering of orbitals for light vs. heavy diatomic molecules, a common high-yield topic in competitive exams.