Which of the following electronic structures refers to transition elements?

Options

A. `2,8,18,5`
B. `2,8,14,2`
C. `2,8,18,32,18,8,1`
D. `2,8,5`

Explanation

To determine which of the given electronic structures refers to transition elements, we need to analyze each option and identify if it corresponds to the general electronic configuration of transition metals, which is characterized by partially filled d-orbitals.

### Step-by-Step Solution:

1. **Understanding Transition Elements:**
Transition elements are defined as d-block elements that have partially filled d-orbitals. The general electronic configuration for transition metals is given as:
\[ [noble gas] \, ns^2 \, (n-1)d^{1-10} \]
where \(n\) is the principal quantum number.

2. **Analyzing Each Option:**
We will analyze each of the provided electronic structures to see if they fit the criteria for transition elements.

**Option A: 2, 8, 18, 5**
- Breakdown:
- 1st shell: 2 electrons (1s²)
- 2nd shell: 8 electrons (2s² 2p⁶)
- 3rd shell: 18 electrons (3s² 3p⁶ 3d¹⁰)
- 4th shell: 5 electrons (4s² 4p³)
- This configuration ends with \(ns^2 np^3\), indicating it is a p-block element (Group 15).
- **Conclusion:** Not a transition element.

**Option B: 2, 8, 14, 2**
- Breakdown:
- 1st shell: 2 electrons (1s²)
- 2nd shell: 8 electrons (2s² 2p⁶)
- 3rd shell: 14 electrons (3s² 3p⁶ 3d⁶)
- 4th shell: 2 electrons (4s²)
- This configuration has 6 electrons in the 3d subshell, indicating it is partially filled.
- **Conclusion:** This is a transition element.

**Option C: 2, 8, 18, 32, 18, 8, 1**
- Breakdown:
- 1st shell: 2 electrons (1s²)
- 2nd shell: 8 electrons (2s² 2p⁶)
- 3rd shell: 18 electrons (3s² 3p⁶ 3d¹⁰)
- 4th shell: 32 electrons (4s² 4p⁶ 4d¹⁰ 4f¹⁴)
- 5th shell: 18 electrons (5s² 5p⁶ 5d¹⁰)
- 6th shell: 8 electrons (6s² 6p⁶)
- 7th shell: 1 electron (7s¹)
- The outermost shell has only 1 electron, indicating it corresponds to an s-block element.
- **Conclusion:** Not a transition element.

**Option D: 2, 8, 5**
- Breakdown:
- 1st shell: 2 electrons (1s²)
- 2nd shell: 8 electrons (2s² 2p⁶)
- 3rd shell: 5 electrons (3s² 3p³)
- This configuration ends with \(ns^2 np^3\), indicating it is a p-block element (Group 15).
- **Conclusion:** Not a transition element.

3. **Final Answer:**
The only option that corresponds to a transition element is **Option B: 2, 8, 14, 2**.