The electrode potential of `M^(2+)//M` of 3d-series elements shows positive value of:

Options

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

Answer

To solve the question regarding the electrode potential of \( M^{2+} // M \) for the 3d-series elements, we will follow these steps:

### Step 1: Identify the 3d-series Elements
The 3d-series elements include:
- Scandium (Sc)
- Titanium (Ti)
- Vanadium (V)
- Chromium (Cr)
- Manganese (Mn)
- Iron (Fe)
- Cobalt (Co)
- Nickel (Ni)
- Copper (Cu)
- Zinc (Zn)

### Step 2: Understand Electrode Potential
Electrode potential refers to the tendency of a chemical species to be reduced, measured in volts. A positive electrode potential indicates a greater tendency to gain electrons (be reduced), while a negative value indicates a lesser tendency.

### Step 3: Refer to the Electrochemical Series
The electrochemical series arranges elements based on their standard electrode potentials. For the 3d-series elements, we can refer to their standard electrode potentials for the \( M^{2+} // M \) half-reaction.

### Step 4: List the Standard Electrode Potentials
The standard electrode potentials for the relevant 3d-series elements are approximately:
- \( \text{Zn}^{2+} + 2e^- \rightarrow \text{Zn} \): \( -0.76 \, \text{V} \)
- \( \text{Fe}^{2+} + 2e^- \rightarrow \text{Fe} \): \( -0.45 \, \text{V} \)
- \( \text{Co}^{2+} + 2e^- \rightarrow \text{Co} \): \( -0.28 \, \text{V} \)
- \( \text{Cu}^{2+} + 2e^- \rightarrow \text{Cu} \): \( +0.34 \, \text{V} \)

### Step 5: Analyze the Values
From the values listed:
- Zinc, Iron, and Cobalt have negative electrode potentials.
- Copper has a positive electrode potential.

### Step 6: Conclusion
The only element from the 3d-series that shows a positive electrode potential when considering the half-reaction \( M^{2+} + 2e^- \rightarrow M \) is Copper (\( \text{Cu} \)).

### Final Answer
The electrode potential of \( M^{2+} // M \) of the 3d-series elements that shows a positive value is **Copper (Cu)**.

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