Consider the following species :
(A) `overset(ө)F" (B) " CH_(3)-overset(ө)(O) " (C) " overset(ө)(C)H_(3) " (D) " overset(ө)(N)H_(2)`
Arrange these species in their decreasing order of nucleophilicity.

Options

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

Answer

To determine the decreasing order of nucleophilicity for the given species, we need to analyze their structure and the factors affecting their nucleophilicity.

### Step-by-Step Solution:

1. **Identify the Species**: The species given are:
- (A) `F^-`
- (B) `CH3O^-`
- (C) `CH3^-`
- (D) `NH2^-`

2. **Understanding Nucleophilicity**: Nucleophilicity is the ability of a species to donate a pair of electrons. It is influenced by:
- Charge: Anions are generally more nucleophilic than neutral species.
- Electronegativity: The more electronegative an atom, the less willing it is to donate electrons.
- Solvent effects: Polar protic solvents can stabilize nucleophiles differently.

3. **Electronegativity Order**: The electronegativity of the atoms involved is crucial. The order of electronegativity for the relevant atoms is:
- F (4.0) > O (3.5) > N (3.0) > C (2.5)

4. **Stability of Negative Charge**: The stability of the negative charge on these species is inversely related to their electronegativity:
- `F^-` is the most stable due to high electronegativity.
- `CH3O^-` is less stable than `F^-` but more stable than `NH2^-`.
- `NH2^-` is less stable than `CH3O^-` but more stable than `CH3^-`.
- `CH3^-` is the least stable and thus the most nucleophilic.

5. **Order of Stability**: Based on the above analysis, the order of stability (from most stable to least stable) is:
- `F^-` > `CH3O^-` > `NH2^-` > `CH3^-`

6. **Order of Nucleophilicity**: The order of nucleophilicity is the reverse of the stability order:
- `CH3^-` > `NH2^-` > `CH3O^-` > `F^-`

7. **Final Arrangement**: Therefore, the decreasing order of nucleophilicity for the given species is:
- (C) `CH3^-` > (D) `NH2^-` > (B) `CH3O^-` > (A) `F^-`

### Final Answer:
The correct order of nucleophilicity is:
(C) `CH3^-` > (D) `NH2^-` > (B) `CH3O^-` > (A) `F^-`