In 3d series, the metal having the highest `M^(2+)//M` standard electrode potential is

Options

A. Cr
B. Fe
C. Cu
D. Zn

Explanation

To determine which metal in the 3D series has the highest standard electrode potential for the reduction of \( M^{2+} \) to \( M \), we need to analyze the standard reduction potentials of the metals in the 3D series. The 3D series includes the transition metals from Scandium (Sc) to Zinc (Zn).

### Step-by-Step Solution:

1. **List the relevant metals in the 3D series**:
The metals we will consider are Scandium (Sc), Titanium (Ti), Vanadium (V), Chromium (Cr), Manganese (Mn), Iron (Fe), Cobalt (Co), Nickel (Ni), Copper (Cu), and Zinc (Zn).

2. **Identify the standard reduction potentials**:
We will focus on the \( M^{2+} \) to \( M \) reduction potentials for the relevant metals:
- \( \text{Zn}^{2+} + 2e^- \rightarrow \text{Zn} \): \( E^\circ = -0.76 \, \text{V} \)
- \( \text{Cr}^{2+} + 2e^- \rightarrow \text{Cr} \): \( E^\circ = -0.91 \, \text{V} \)
- \( \text{Cu}^{2+} + 2e^- \rightarrow \text{Cu} \): \( E^\circ = +0.34 \, \text{V} \)
- \( \text{Fe}^{2+} + 2e^- \rightarrow \text{Fe} \): \( E^\circ = +0.44 \, \text{V} \)
- Other metals like Ni, Co, and Mn have potentials that are lower than Cu and Fe.

3. **Compare the standard reduction potentials**:
From the values obtained:
- \( \text{Zn}^{2+} \): -0.76 V
- \( \text{Cr}^{2+} \): -0.91 V
- \( \text{Cu}^{2+} \): +0.34 V
- \( \text{Fe}^{2+} \): +0.44 V

The highest standard reduction potential among these is for Copper (\( \text{Cu}^{2+} \)) at +0.34 V, followed by Iron (\( \text{Fe}^{2+} \)) at +0.44 V.

4. **Conclusion**:
Therefore, the metal having the highest \( M^{2+}/M \) standard electrode potential in the 3D series is **Copper (Cu)**.

### Final Answer:
**Copper (Cu)** has the highest \( M^{2+}/M \) standard electrode potential in the 3D series.