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

Options

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

Answer

To solve the question regarding the maximum and minimum melting points of the first and second transition series, we will analyze the properties of the transition metals and their melting points.

### Step-by-Step Solution:

1. **Understanding Transition Metals:**
Transition metals are elements that have partially filled d-orbitals. Their melting points can vary significantly due to the strength of the metallic bonds formed by the presence of unpaired electrons.

**Hint:** Remember that the presence of unpaired electrons contributes to stronger metallic bonding.

2. **Melting Points Trend:**
In transition metals, the melting points generally increase up to the middle of the series and then decrease. This is due to the pairing of electrons in the d-orbitals, which weakens the metallic bond.

**Hint:** Consider how electron pairing affects the strength of metallic bonds.

3. **Identifying Maximum Melting Point in the First Transition Series:**
Among the first transition series (Scandium to Zinc), Chromium (Cr) is known to have one of the highest melting points. This is attributed to its electronic configuration, which allows for a high degree of metallic bonding due to unpaired electrons.

**Hint:** Look for the element in the first transition series with a high melting point, typically around the middle of the series.

4. **Identifying Minimum Melting Point in the Second Transition Series:**
In the second transition series (Yttrium to Cadmium), Cadmium (Cd) has one of the lowest melting points. This is due to its filled d-orbitals, which result in weaker metallic bonding.

**Hint:** Identify the element in the second transition series that is known for having a low melting point.

5. **Conclusion:**
Based on the analysis:
- The maximum melting point in the first transition series is observed with Chromium (Cr).
- The minimum melting point in the second transition series is observed with Cadmium (Cd).

Therefore, the correct answer to the question is **Chromium and Cadmium**.

### Final Answer:
The maximum and minimum melting points of the first and second transition series respectively are observed with **Chromium and Cadmium**.