JEE Main 2026 Chemistry 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:
Answer: (D)
Solution
Eu is 4f⁷, Gd is 4f⁷5d¹ (4f⁷): same 4f count. Yb is 4f¹⁴, Hf is [Xe]4f¹⁴5d²6s² (4f¹⁴): same. Dy(4f¹⁰)≠Ho(4f¹¹); Lu(4f¹⁴)≠Tm(4f¹³).