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JEE Main2026Apr 4, Shift 2Chemistry
Q.

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:

  1. A

    B and C Only

  2. B

    A and B Only

  3. C

    A and D Only

  4. D

    A and C Only

Solution

Write out 4f populations:

Eu (Z=63): [Xe] 4f 6s — 4f.

Gd (Z=64): [Xe] 4f 5d 6s — 4f (half-filled stability).

Dy (Z=66): [Xe] 4f 6s — 4f.

Ho (Z=67): [Xe] 4f 6s — 4f.

Yb (Z=70): [Xe] 4f 6s — 4f.

Lu (Z=71): [Xe] 4f 5d 6s — 4f.

Hf (Z=72): [Xe] 4f 5d 6s — 4f.

Tm (Z=69): [Xe] 4f 6s — 4f.

Pairs with equal 4f populations: A (Eu, Gd: both 4f) and C (Yb, Hf: both 4f).

A and C only.

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