The maximum and minimum melting points of first and second transition series respectively are observed with

Options

A. Cr and Zn
B. Cr and Cd
C. Cr and Hg
D. Mo and Cd

Answer

To solve the question regarding the maximum and minimum melting points of the first and second transition series, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Elements**:
- We need to find the elements in the first transition series (which includes Scandium to Zinc) and the second transition series (which includes Yttrium to Cadmium).

2. **Determine the Melting Points**:
- The maximum melting point in the first transition series is typically observed in Chromium (Cr), while the minimum melting point is found in Zinc (Zn).
- For the second transition series, the maximum melting point is observed in Molybdenum (Mo), and the minimum melting point is in Cadmium (Cd).

3. **Analyze Electronic Configurations**:
- For Chromium (Cr), the electronic configuration is [Ar] 4s¹ 3d⁵. This half-filled configuration allows for strong metallic bonding, leading to a high melting point.
- For Zinc (Zn), the electronic configuration is [Ar] 4s² 3d¹⁰. The fully filled orbitals do not contribute to metallic bonding strength, resulting in a lower melting point.
- For Cadmium (Cd), the electronic configuration is [Kr] 5s² 4d¹⁰. Similar to Zinc, the fully filled orbitals do not participate in bonding, leading to a low melting point.

4. **Conclude the Answer**:
- Therefore, the maximum melting point in the first transition series is observed with Chromium (Cr) and the minimum melting point in the second transition series is observed with Cadmium (Cd).

5. **Final Answer**:
- The correct answer is: Chromium (Cr) and Cadmium (Cd).