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 gtb`
C. `c gt a gt b gtd`
D. `c gta gtd gtb`

Explanation

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

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

- In this reaction, C is oxidized to C^+ while B^+ is reduced to B.
- Since C is able to reduce B^+, it indicates that C is a good reducing agent.

### Step 2: Analyze Reaction (ii)
**Reaction:** \( A^- + D \rightarrow \) NO reaction

- The lack of reaction suggests that A^- cannot reduce D.
- This implies that D is not a good oxidizing agent compared to A^- or that A^- is not a strong enough reducing agent to reduce D.

### Step 3: Analyze Reaction (iii)
**Reaction:** \( C^+ + A \rightarrow \) NO reaction

- Again, the lack of reaction indicates that A cannot reduce C^+.
- This suggests that A is not a strong enough reducing agent compared to C^+.

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

- In this reaction, D is oxidized to D^+ while B^+ is reduced to B.
- This indicates that D is a good reducing agent since it can reduce B^+.

### Step 5: Summarize Reducing Powers
From the analysis of the reactions, we can summarize the reducing abilities:
- From Reaction (i): C is a better reducing agent than B.
- From Reaction (ii): A is a better reducing agent than D (since A^- does not reduce D).
- From Reaction (iii): C is a better reducing agent than A.
- From Reaction (iv): D is a better reducing agent than B.

### Step 6: Establish Order of Reducing Agents
Based on the above deductions:
1. C > A (from Reaction iii)
2. A > D (from Reaction ii)
3. D > B (from Reaction iv)
4. C > B (from Reaction i)

Combining these relationships, we can establish the order of reducing agents:
- C is the strongest reducing agent.
- A is the next strongest.
- D follows.
- B is the weakest reducing agent.

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

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