JEE Main · 2024 · Shift-ImediumATOM-097

Which of the following electronic configuration would be associated with the highest magnetic moment?

Structure of Atom · Class 11 · JEE Main Previous Year Question

Question

Which of the following electronic configuration would be associated with the highest magnetic moment?

Options
  1. a

    [Ar] 3d7[\text{Ar}]\,3d^7

  2. b

    [Ar] 3d8[\text{Ar}]\,3d^8

  3. c

    [Ar] 3d3[\text{Ar}]\,3d^3

  4. d

    [Ar] 3d6[\text{Ar}]\,3d^6

    ✓
Correct Answerd

[Ar] 3d6[\text{Ar}]\,3d^6

Detailed Solution

🧠 The Unpaired Electron Peak Magnetic moment (mu=sqrtn(n+2)mu = sqrt{n(n+2)}) is driven entirely by unpaired electrons. The more "lonely" electrons a subshell has, the stronger the magnetic "pull" it exerts.

🗺️ The Configuration Audit Using Hund's Rule for the 3d subshell (5 rooms):

  • (a) 3d73d^7: 5 up, 2 down →\to 3 unpaired.
  • (b) 3d83d^8: 5 up, 3 down →\to 2 unpaired.
  • (c) 3d33d^3: 3 up →\to 3 unpaired.
  • (d) 3d63d^6: 5 up, 1 down →\to 4 unpaired.
  • The Winner: 3d63d^6 has the highest count (n=4n=4).

⚡ The "Center-Point" Trick Unpaired electrons peak at d5d^5 (5 unpaired). As you go past 55, pairing starts and magnetic moment drops. So d4d^4 or d6d^6 will always beat d7,d8,d9d^7, d^8, d^9.

⚠️ Common Traps Many students count total electrons instead of unpaired ones. Remember: paired electrons cancel each other out (+1/2+1/2 and −1/2-1/2).

Answer: (d)\boxed{\text{Answer: (d)}}

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