Question

Consider the elements with atomic numbers Z = 1 to Z=20. The number of elements with only one unpaired electron in their ground state is

• A. 10
• B. 6
• C. 8
• D. 12

Hint:

The elements with one unpaired electron are typically in Group 1 (alkali metals), Group 13 (Boron group), and Group 17 (halogens). Quickly identifying these groups can help you count the elements faster.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
Count elements Z=1 to 20 with exactly one unpaired electron.

Step 2: Key Concept (Alternate):
Check electron configuration of each. One unpaired = ns¹, np¹, or np⁵.

Step 3: Detailed Explanation:
H(1s¹), Li(2s¹), B(2p¹), F(2p⁵), Na(3s¹), Al(3p¹), Cl(3p⁵), K(4s¹). Total 8 elements.

Step 4: Final Answer:
8 elements have exactly one unpaired electron.