Question

Pairs of elements with the same number of electrons in their respective 4f orbital are
[Atomic number: Eu-63, Gd-64, Dy-66, Ho-67, Tm-69, Yb-70, Lu-71, Hf-72]
A. (Eu and Gd)
B. (Dy and Ho)
C. (Yb and Hf)
D. (Lu and Tm)
Choose the correct answer from the options given below:

• A. B and C Only
• B. A and B Only
• C. A and D Only
• D. A and C Only

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
The electronic configurations of lanthanides follow the \( 4f \) filling. Half-filled (\( 4f^7 \)) and fully-filled (\( 4f^{14} \)) shells provide extra stability. In Gd and Lu, an electron is placed in the \( 5d \) orbital instead of \( 4f \) to preserve this stability.

Step 2: Key Formula or Approach:
Write general configuration: \( [Xe] 4f^n 5d^x 6s^2 \). Determine \( n \) for each element.

Step 3: Detailed Explanation:
- Eu (63): \( [Xe] 4f^7 6s^2 \). (f electrons = 7)
- Gd (64): \( [Xe] 4f^7 5d^1 6s^2 \). (f electrons = 7). A is a match.
- Dy (66): \( [Xe] 4f^{10} 6s^2 \). (f electrons = 10)
- Ho (67): \( [Xe] 4f^{11} 6s^2 \). (f electrons = 11). B is not a match.
- Tm (69): \( [Xe] 4f^{13} 6s^2 \). (f electrons = 13)
- Yb (70): \( [Xe] 4f^{14} 6s^2 \). (f electrons = 14)
- Lu (71): \( [Xe] 4f^{14} 5d^1 6s^2 \). (f electrons = 14)
- Hf (72): \( [Xe] 4f^{14} 5d^2 6s^2 \). (f electrons = 14). C is a match (Yb and Hf).
Comparing pairs: A matches (7 each) and C matches (14 each).

Step 4: Final Answer:
Pairs A and C have the same number of 4f electrons.