Which of the following is arranged in order of incresing melting point ?

Options

A. Zn < Cu < Ni < Fe
B. Fe < Ni < Cu < Zn
C. `NiltFeltZnltCu`
D. Cu < Zn < Fe < Ni

Answer

To determine the order of increasing melting points for the given transition metals (iron, nickel, copper, and zinc), we will analyze the number of unpaired electrons in each metal, as the melting point is directly related to the strength of the metallic bond, which in turn is influenced by the number of unpaired electrons.

### Step-by-Step Solution:

1. **Identify the Elements**: The elements we are considering are Iron (Fe), Nickel (Ni), Copper (Cu), and Zinc (Zn).

2. **Determine Electronic Configurations**:
- **Iron (Fe)**: The electronic configuration is [Ar] 4s² 3d⁶.
- **Nickel (Ni)**: The electronic configuration is [Ar] 4s² 3d⁸.
- **Copper (Cu)**: The electronic configuration is [Ar] 4s² 3d¹⁰.
- **Zinc (Zn)**: The electronic configuration is [Ar] 4s² 3d¹⁰.

3. **Count the Number of Unpaired Electrons**:
- **Iron (Fe)**: In the 3d subshell, there are 6 electrons. The arrangement is: ↑↓ ↑ ↑ ↑ (4 unpaired electrons).
- **Nickel (Ni)**: In the 3d subshell, there are 8 electrons. The arrangement is: ↑↓ ↑ ↑ ↑ ↑ (2 unpaired electrons).
- **Copper (Cu)**: In the 3d subshell, there are 10 electrons, which means all are paired (0 unpaired electrons).
- **Zinc (Zn)**: Similar to Copper, Zinc has a fully filled 3d subshell with 10 electrons (0 unpaired electrons).

4. **Rank the Elements by Number of Unpaired Electrons**:
- Iron (Fe) has 4 unpaired electrons.
- Nickel (Ni) has 2 unpaired electrons.
- Copper (Cu) has 1 unpaired electron.
- Zinc (Zn) has 0 unpaired electrons.

5. **Determine the Order of Melting Points**:
- The melting point increases with the number of unpaired electrons due to stronger metallic bonds.
- Therefore, the order of increasing melting points is:
- Zinc (0 unpaired electrons) < Copper (1 unpaired electron) < Nickel (2 unpaired electrons) < Iron (4 unpaired electrons).

6. **Final Answer**:
- The increasing order of melting points is: **Zinc < Copper < Nickel < Iron**.