Zn, Cd, Hg have lowest melting points in their respective periods. This can be explained based on

Options

A. electrons used for bonding
B. charges present in nucleus
C. defects is crystal structures
D. conducting properties

Answer

To explain why Zn, Cd, and Hg have the lowest melting points in their respective periods, we can follow these steps:

### Step 1: Identify the Elements and Their Electronic Configurations
- **Zinc (Zn)**: Atomic number 30, electronic configuration: [Ar] 3d10 4s2
- **Cadmium (Cd)**: Atomic number 48, electronic configuration: [Kr] 4d10 5s2
- **Mercury (Hg)**: Atomic number 80, electronic configuration: [Xe] 4f14 5d10 6s2

### Step 2: Analyze the Electronic Configurations
- All three elements have completely filled d-orbitals (3d10, 4d10, and 5d10) and s-orbitals (4s2, 5s2, and 6s2).
- The presence of paired electrons in these orbitals means that there are no unpaired electrons available for bonding.

### Step 3: Understand the Importance of Unpaired Electrons in Bonding
- Metals typically bond through metallic bonding, which involves the sharing of unpaired electrons.
- The absence of unpaired electrons in Zn, Cd, and Hg leads to weaker metallic bonds.

### Step 4: Relate Bonding Strength to Melting Points
- Weaker metallic bonds result in lower melting points because less energy is required to break these bonds.
- Therefore, the melting points of Zn, Cd, and Hg are lower compared to other transition metals in their respective periods.

### Step 5: Conclusion
- The low melting points of Zn, Cd, and Hg can be explained by the fact that the electrons used for bonding are all paired, leading to weak bonding and thus lower melting points.

### Final Answer
The correct explanation for why Zn, Cd, and Hg have the lowest melting points in their respective periods is based on the **electrons used for bonding**.

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