Question

Observe the elements from H(Z=1) to Ca(Z=20). The number of elements with 1, 2 and 3 unpaired electrons in their ground state is respectively

• A. 2, 4, 8
• B. 6, 8, 4
• C. 6, 4, 2
• D. 8, 4, 2

Hint:

Use periodic table trends: s-block odd Z have 1 unpaired, p-block count based on valence. Hund's rule maximizes unpaired in ground state. List configurations for accuracy.

Answer 1

The Correct Option is D

1. Unpaired electrons are determined from ground-state electron configurations using Hund's rule.
2. Elements with 1 unpaired: s^1 (H, Li, Na, K) and p^1 (B, Al), p^5 (F, Cl) – total 8.
3. Elements with 2 unpaired: p^2 (C, Si), p^4 (O, S) – total 4.
4. Elements with 3 unpaired: p^3 (N, P) – total 2.
5. Note: No d-electrons up to Ca (Z=20); Ca has 0 unpaired (4s^2).
6. Therefore, the correct option is (4) 8, 4, 2.