The melting point of `Zn` is lower as compared to those of the other elements of `3d` series because:

Options

A. The orbitals are completely filled.
B. the d-orbitals are partially filled
C. d-electrons do not participate in metallic bonding
D. size of `Zn` atoms is smaller

Explanation

To solve the question regarding why the melting point of zinc (Zn) is lower compared to other elements of the 3d series, we can follow these steps:

### Step 1: Understand the Electronic Configuration of Zinc
Zinc has an atomic number of 30. Its electronic configuration can be written as:
\[ \text{Zn: } [\text{Ar}] 3d^{10} 4s^2 \]
This shows that zinc has a completely filled 3d subshell (10 electrons) and a filled 4s subshell (2 electrons).

**Hint:** Remember that the arrangement of electrons in an atom can influence its physical properties, including melting point.

### Step 2: Identify the Importance of Unpaired Electrons
In transition metals, the presence of unpaired electrons in the d orbitals contributes to the strength of metallic bonding. Metals with unpaired electrons can form stronger metallic bonds due to increased interactions between the delocalized electrons and the positively charged metal ions (kernels).

**Hint:** Unpaired electrons play a crucial role in determining the strength of metallic bonds.

### Step 3: Analyze the Metallic Bonding in Zinc
Since zinc has a completely filled 3d and 4s subshell, it does not have any unpaired electrons. This results in fewer delocalized electrons available to participate in metallic bonding compared to other transition metals that have unpaired electrons.

**Hint:** Consider how the presence or absence of unpaired electrons affects the overall bonding in metals.

### Step 4: Conclude the Effect on Melting Point
The weaker metallic bonds in zinc, due to the absence of unpaired electrons, lead to a lower melting point compared to other elements in the 3d series, which typically have unpaired electrons and thus stronger metallic bonds.

**Hint:** Think about how the strength of bonds relates to the energy required to change a solid into a liquid (melting).

### Final Conclusion
The melting point of zinc is lower than that of other 3d transition metals because it has completely filled d and s orbitals, resulting in no unpaired electrons and consequently weaker metallic bonds.

### Summary of Key Points
1. Zinc's electronic configuration is \([Ar] 3d^{10} 4s^2\).
2. It has no unpaired electrons, leading to weaker metallic bonding.
3. Weaker metallic bonds result in a lower melting point compared to other 3d transition metals.