Arrange the following in decreasing order of basic strenth.
`underset(I)(CI^(-)) underset(II)(RCOO^(-)) underset(III)(OH^(-)) underset(IV)(RO^(-)) underset(V)(NH^(-))`

Options

A. `IgtIIltIIIgtIVltV`
B. `VgtIVgtIIgtIIIgtI`
C. `IgtIIgtIIIgtIVgtV`
D. `VgtIVgtIIIgtIIgtI`

Answer

To arrange the given ions in decreasing order of basic strength, we need to analyze the basicity of each ion based on their structures and the stability of their negative charges. Here’s a step-by-step solution:

### Step 1: Identify the Ions
The ions given are:
1. \( \text{I} \) - \( \text{Cl}^- \)
2. \( \text{II} \) - \( \text{RCOO}^- \) (carboxylate ion)
3. \( \text{III} \) - \( \text{OH}^- \) (hydroxide ion)
4. \( \text{IV} \) - \( \text{RO}^- \) (alkoxide ion)
5. \( \text{V} \) - \( \text{NH}_2^- \) (amide ion)

### Step 2: Analyze Basicity
- **Basicity** is the ability of a species to donate a pair of electrons. The more stable the negative charge, the less basic the ion will be.

1. **\( \text{NH}_2^- \)**: This ion is very basic because the negative charge is localized on nitrogen, which is less electronegative than oxygen and can effectively donate its electron pair.

2. **\( \text{RO}^- \)**: The alkoxide ion is also quite basic. The negative charge is localized on oxygen, but it is less stable than \( \text{NH}_2^- \) due to the electronegativity of oxygen.

3. **\( \text{OH}^- \)**: The hydroxide ion is less basic than alkoxides because it is more stable due to resonance and the electronegativity of oxygen.

4. **\( \text{RCOO}^- \)**: The carboxylate ion has resonance stabilization, which delocalizes the negative charge, making it less basic than hydroxide and alkoxide ions.

5. **\( \text{Cl}^- \)**: The chloride ion is the least basic among the given ions because it is a stable ion with a high electronegativity, making it less willing to donate its electron pair.

### Step 3: Arrange in Decreasing Order of Basic Strength
Based on the analysis:
1. \( \text{NH}_2^- \) (most basic)
2. \( \text{RO}^- \)
3. \( \text{OH}^- \)
4. \( \text{RCOO}^- \)
5. \( \text{Cl}^- \) (least basic)

### Final Order
Thus, the decreasing order of basic strength is:
\[ \text{NH}_2^- > \text{RO}^- > \text{OH}^- > \text{RCOO}^- > \text{Cl}^- \]