Question

The number of d-electrons in Fe²⁺ (Z = 26) is not equal to:

• A. the number of p-electrons in Ne (Z = 10)
• B. the number of s-electrons in Mg (Z = 12)
• C. the number of d-electrons in Fe (Z = 26)
• D. the number of p-electrons in Cl (Z = 17)

Hint:

Determine the electron configuration of ions by removing electrons from the outermost shell first. Compare the specific electron types (s, p, d) as asked.

Answer 1

The Correct Option is D

Fe$^{2+}$ (Z = 26): Electron configuration of Fe is [Ar] 4s$^2$ 3d$^6$. 
For Fe$^{2+}$, remove 2 electrons from 4s: [Ar] 3d$^6$. 
Number of d-electrons = 6. 
Option 1: Ne (Z = 10): 1s$^2$ 2s$^2$ 2p$^6$. p-electrons = 6 (matches). 
Option 2: Mg (Z = 12): 1s$^2$ 2s$^2$ 2p$^6$ 3s$^2$. s-electrons = 6 (matches). 
Option 3: Fe (Z = 26): [Ar] 4s$^2$ 3d$^6$. d-electrons = 6 (matches). 
Option 4: Cl (Z = 17): 1s$^2$ 2s$^2$ 2p$^6$ 3s$^2$ 3p$^5$. p-electrons = 11 (does not match). 
Thus, the number of d-electrons in Fe$^{2+}$ is not equal to the number of p-electrons in Cl.