Standard electrode potentials of redox couples `A^(2+)//A, B^(2+)//B, C//C^(2+)" and "D^(2+)//D` are 0.3 V, -0.5 V, -0.75 V and 0.9 V respectively. Which of these is best oxidising agent and reducing agent respectively?

Options

A. `D^(2+)//D" and "B^(2+)//B`
B. `B^(2+)//B" and "D^(2+)//D`
C. `D^(2+)//D" and "C^(2+)//C`
D. `C^(2+)//C" and "D^(2+)//D`

Answer

To determine the best oxidizing and reducing agents from the given standard electrode potentials of the redox couples, we can follow these steps:

### Step 1: List the Standard Electrode Potentials
We have the following standard electrode potentials for the redox couples:
- \( A^{2+} // A \): \( E^\circ = 0.3 \, \text{V} \)
- \( B^{2+} // B \): \( E^\circ = -0.5 \, \text{V} \)
- \( C // C^{2+} \): \( E^\circ = -0.75 \, \text{V} \)
- \( D^{2+} // D \): \( E^\circ = 0.9 \, \text{V} \)

### Step 2: Identify the Best Oxidizing Agent
The best oxidizing agent corresponds to the highest standard reduction potential. From the values listed:
- The highest potential is \( 0.9 \, \text{V} \) for the couple \( D^{2+} // D \).

Thus, the best oxidizing agent is:
- **Best Oxidizing Agent: \( D^{2+} \)**

### Step 3: Identify the Best Reducing Agent
The best reducing agent corresponds to the lowest standard reduction potential. From the values listed:
- The lowest potential is \( -0.75 \, \text{V} \) for the couple \( C // C^{2+} \).

Thus, the best reducing agent is:
- **Best Reducing Agent: \( C \)**

### Final Answer
- **Best Oxidizing Agent: \( D^{2+} \)**
- **Best Reducing Agent: \( C \)**