Question

What is the atomic number of an element having \(ns^1\) electronic configuration and belonging to 3d transition series?

• A. Only 24
• B. Only 25
• C. Only 29
• D. 24 and 29

Hint:

Chromium and copper have \(4s^1\) because of the extra stability of half-filled and full d subshells.

Answer 1

The Correct Option is D

Step 1: Plan:
List the 3d series and check each configuration.

Step 2: Steps:
Sc $3d^14s^2$, Ti $3d^24s^2$, V $3d^34s^2$, Cr $3d^54s^1$, Mn $3d^54s^2$, Fe $3d^64s^2$, Co $3d^74s^2$, Ni $3d^84s^2$, Cu $3d^{10}4s^1$, Zn $3d^{10}4s^2$.
Only Cr and Cu break the $4s^2$ pattern, so the atomic numbers are $24$ and $29$.

Final Answer:
The atomic numbers are $24$ and $29$, option (D). \[ \boxed{24\ \text{and}\ 29} \]