Given the following reaction involving A,B,C and D
(i) `C+B^(+) rarr C^(+)+B`
(ii) `A^(-)+D rarr` NO reaction
(iii) `C^(+)+A rarr` NO reaction
(iv) `D+B^(+) rarr D^(+)+B`
the correct arrangement of A,B,C,D in the order of their decreasing ability as reducing agent

Options

A. `D gt B gt C gt A`
B. `A gt C gt D gt B`
C. `C gt A gt B gt D`
D. `C gt A gt D gt B`

Answer

To determine the correct arrangement of A, B, C, and D in order of their decreasing ability as reducing agents, we will analyze each of the given reactions step by step.

### Step 1: Analyze the First Reaction
**Reaction:** \( C + B^+ \rightarrow C^+ + B \)

- In this reaction, \( B^+ \) (which is in the +1 oxidation state) is reduced to \( B \) (0 oxidation state).
- Since \( C \) is oxidized to \( C^+ \), it acts as a reducing agent.
- **Conclusion:** \( C \) is a stronger reducing agent than \( B \).
- **Result:** \( C > B \)

### Step 2: Analyze the Second Reaction
**Reaction:** \( A^- + D \rightarrow \) No reaction

- The lack of reaction indicates that \( D \) cannot reduce \( A^+ \) to \( A \).
- This implies that \( D \) has less reducing power compared to \( A \).
- **Conclusion:** \( A \) is a stronger reducing agent than \( D \).
- **Result:** \( A > D \)

### Step 3: Analyze the Third Reaction
**Reaction:** \( C^+ + A \rightarrow \) No reaction

- Again, the absence of a reaction indicates that \( A \) cannot reduce \( C^+ \) to \( C \).
- This means \( C \) has a higher reducing power than \( A \).
- **Conclusion:** \( C \) is a stronger reducing agent than \( A \).
- **Result:** \( C > A \)

### Step 4: Analyze the Fourth Reaction
**Reaction:** \( D + B^+ \rightarrow D^+ + B \)

- Here, \( B^+ \) is reduced to \( B \) by \( D \).
- This indicates that \( D \) has a higher reducing power than \( B \).
- **Conclusion:** \( D \) is a stronger reducing agent than \( B \).
- **Result:** \( D > B \)

### Step 5: Combine the Results
From the conclusions drawn from each reaction, we have:
1. \( C > B \) (from Step 1)
2. \( A > D \) (from Step 2)
3. \( C > A \) (from Step 3)
4. \( D > B \) (from Step 4)

Now, we can summarize the relationships:
- From \( C > A \) and \( A > D \), we can conclude \( C > A > D \).
- From \( D > B \), we can include \( B \) in the hierarchy.

Thus, we can arrange the reducing agents in the order of their decreasing ability:
- \( C > A > D > B \)

### Final Answer
The correct arrangement of A, B, C, and D in the order of their decreasing ability as reducing agents is:
**C > A > D > B**