Question

Consider the following elements. Hf \([Z = 72]\) ; Yb \([Z = 70]\) ; Lu \([Z = 71]\) Gd \([Z = 64]\) ; Eu \([Z = 63]\) ; Tm \([Z = 69]\) Dy \([Z = 66]\) ; Er \([Z = 68]\) A : [Hf, Yb] B : [Gd, Eu] C : [Lu, Tm] D : [Er, Dy] The pair which contains same number of \(f\) electrons.

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

Answer 1

The Correct Option is A

To determine which pair contains the same number of \(f\) electrons, we need to analyze the electronic configurations of the given elements. Specifically, we focus on the \(f\) subshell as the question is about the number of \(f\) electrons.

Let's examine the electronic configuration of each element:

1. Hf (\([Z = 72]\)): Electronic configuration is \([Xe] 4f^{14} 5d^{2} 6s^{2}\). The number of \(4f\) electrons is 14.
2. Yb (\([Z = 70]\)): Electronic configuration is \([Xe] 4f^{14} 6s^{2}\). The number of \(4f\) electrons is 14.
3. Lu (\([Z = 71]\)): Electronic configuration is \([Xe] 4f^{14} 5d^{1} 6s^{2}\). The number of \(4f\) electrons is 14.
4. Gd (\([Z = 64]\)): Electronic configuration is \([Xe] 4f^{7} 5d^{1} 6s^{2}\). The number of \(4f\) electrons is 7.
5. Eu (\([Z = 63]\)): Electronic configuration is \([Xe] 4f^{7} 6s^{2}\). The number of \(4f\) electrons is 7.
6. Tm (\([Z = 69]\)): Electronic configuration is \([Xe] 4f^{13} 6s^{2}\). The number of \(4f\) electrons is 13.
7. Dy (\([Z = 66]\)): Electronic configuration is \([Xe] 4f^{10} 6s^{2}\). The number of \(4f\) electrons is 10.
8. Er (\([Z = 68]\)): Electronic configuration is \([Xe] 4f^{12} 6s^{2}\). The number of \(4f\) electrons is 12.

Now, let's group them according to the options and see which has the same number of \(f\) electrons:

• A: [Hf, Yb] - Number of \(f\) electrons: \(14\) and \(14\) respectively.
• B: [Gd, Eu] - Number of \(f\) electrons: \(7\) and \(7\) respectively.
• C: [Lu, Tm] - Number of \(f\) electrons: \(14\) and \(13\) respectively.
• D: [Er, Dy] - Number of \(f\) electrons: \(12\) and \(10\) respectively.

From the data above, pairs A and B each have elements with the same number of \(f\) electrons.

Conclusion: The correct answer is A and B, as both pairs have elements with the same number of \(f\) electrons.