Based on the following information arrange four metals `A,B,C` and `D` in order of decreasing ability to act as reducing agents `:`
`(I)` Only A,B, and C react with `1M HCl` to give `H_(2)(g)`
`(II)` When C is added to solutions of the other metal ions, metallic B and D are formed
`(III)` Metal C does not reduced `A^(n+)`

Options

A. `CgtAgtBgtD`
B. `CgtAgtDgtB`
C. `AgtCgtDgtB`
D. `AgtCgtBgtD`

Answer

To arrange the metals A, B, C, and D in order of decreasing ability to act as reducing agents, we can analyze the information provided step by step.

### Step 1: Analyze the reaction with HCl
From the first piece of information, we know that only metals A, B, and C react with 1M HCl to produce hydrogen gas. This indicates that these metals can act as reducing agents since they can reduce hydrogen ions (H⁺) to hydrogen gas (H₂). The metal that reacts will be oxidized in the process.

**Hint:** Metals that react with acids to produce hydrogen are likely good reducing agents.

### Step 2: Determine the reactivity of D
Since D does not react with HCl, we can conclude that D has the least ability to act as a reducing agent among the four metals. Therefore, D will be placed last in our order.

**Hint:** If a metal does not react with an acid, it is likely a poor reducing agent.

### Step 3: Analyze the displacement reaction involving C
The second piece of information states that when C is added to solutions of other metal ions, metallic B and D are formed. This means that C is able to displace both B and D from their ionic forms, indicating that C is more reactive than both B and D.

**Hint:** A metal that can displace others from their solutions is more reactive than those metals.

### Step 4: Analyze the inability of C to reduce A
The third piece of information tells us that metal C does not reduce A⁺. This implies that A is more reactive than C, as C cannot displace A from its ionic form.

**Hint:** If a metal cannot reduce another metal ion, it is less reactive than that metal.

### Step 5: Establish the order of reducing ability
From the analysis:
- A is more reactive than C (C cannot reduce A).
- C is more reactive than B and D (C can displace B and D).
- D is the least reactive since it does not react with HCl.

Thus, we can arrange the metals in order of decreasing ability to act as reducing agents:
1. A (most reactive)
2. C
3. B
4. D (least reactive)

### Final Order
The final order of decreasing ability to act as reducing agents is:
**A > C > B > D**

### Summary of the Solution
1. A, B, and C react with HCl; D does not.
2. C can displace B and D from their solutions.
3. C cannot reduce A, indicating A is more reactive than C.
4. Therefore, the order is A, C, B, D.