Question

High second ionization enthalpies than expected are observed for

• A. Ti, Zn
• B. Mn, Fe
• C. V, Ni
• D. Cr, Cu

Hint:

Exceptionally stable half-filled \((d^5)\) and fully filled \((d^{10})\) configurations lead to unusually high ionization enthalpies when an electron has to be removed from them.

Answer 1

The Correct Option is D

Step 1: Inspect the stability of singly charged ions.
Cr: [Ar]3d⁵4s¹ → Cr⁺: 3d⁵ (half-filled, very stable). Cu: [Ar]3d¹⁰4s¹ → Cu⁺: 3d¹⁰ (fully filled, very stable). Ionizing these stable M⁺ ions further demands much more energy, causing anomalously high second ionization enthalpies.

Step 2: Final Answer:
Cr and Cu (option 4).