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] Choose the correct answer from the options given below :
- B and C Only
- A and B Only
- A and D Only
- A and C Only
Answer
(4) A and C Only
Solution
Electronic configurations ([Xe] core):
Eu (63): 4f7 6s2 → 7; Gd (64): 4f7 5d1 6s2 → 7 ⇒ A ✓ (stable half-filled 4f)
Dy (66): 4f10 6s2 → 10; Ho (67): 4f11 6s2 → 11 ⇒ B ✗
Yb (70): 4f14 6s2 → 14; Hf (72): 4f14 5d2 6s2 → 14 ⇒ C ✓
Lu (71): 4f14 5d1 6s2 → 14; Tm (69): 4f13 6s2 → 13 ⇒ D ✗
∴ A and C
Answer: (4)