In the first row of the d block (transition metals), how many elements exhibit exceptions to the standard electron configuration due to increased stability of half-filled or fully filled d subshells?

• A. 2
• B. 1
• C. 0
• D. 3

Answer: (A)

Verified step by step guidance

1. Identify the elements in the first row of the d block, which are the transition metals from Scandium (Sc, atomic number 21) to Zinc (Zn, atomic number 30).
2. Recall the standard electron configuration filling order for these elements, which generally follows the pattern: \((n-1)d^{1-10} ns^{2}\), where \(n=4\) for the first d-block row.
3. Understand that exceptions to the standard electron configuration occur when an element gains extra stability by having a half-filled (\(d^5\)) or fully filled (\(d^{10}\)) d subshell, often by moving one electron from the \(ns\) orbital to the \(d\) orbital.
4. Identify the specific elements in this row that exhibit such exceptions: Chromium (Cr) and Copper (Cu). Chromium has an electron configuration of \([Ar] 3d^5 4s^1\) instead of \$3d^4 4s^2\(, and Copper has \)[Ar] 3d^{10} 4s^1\( instead of \)3d^9 4s^2$.
5. Count these elements to find that there are 2 elements in the first d-block row that show exceptions due to increased stability of half-filled or fully filled d subshells.