Arrang the anions (p) `overset(-)CH_(3),(q)overset(-)NH_(2),(r)OH^(-), (s)F^(-),` in decreasing order of their basic strength .

Options

A. `p gt q gt gt r gt s `
B. `q gt p gt r gt s`
C. `r gt q gt p gt s`
D. `r gt p gt q gt s`

Answer

To arrange the anions \( \overset{-}{CH_3}, \overset{-}{NH_2}, OH^{-}, F^{-} \) in decreasing order of their basic strength, we need to analyze their ability to accept protons. The stronger the base, the more readily it will accept a proton.

### Step-by-step Solution:

1. **Identify the Conjugate Acids**:
- For \( \overset{-}{CH_3} \) (methyl anion), the conjugate acid is \( CH_4 \) (methane).
- For \( \overset{-}{NH_2} \) (amide ion), the conjugate acid is \( NH_3 \) (ammonia).
- For \( OH^{-} \) (hydroxide ion), the conjugate acid is \( H_2O \) (water).
- For \( F^{-} \) (fluoride ion), the conjugate acid is \( HF \) (hydrofluoric acid).

2. **Determine the Strength of the Conjugate Acids**:
- The strength of acids can be compared based on their ability to donate protons. The stronger the acid, the weaker its conjugate base.
- The order of acidic strength is:
- \( CH_4 < NH_3 < H_2O < HF \)
- This means \( CH_4 \) is the weakest acid and \( HF \) is the strongest acid.

3. **Relate Acid Strength to Base Strength**:
- Since stronger acids have weaker conjugate bases, we can deduce the order of basic strength from the order of acidic strength:
- \( \overset{-}{CH_3} \) is the strongest base (weakest acid),
- \( \overset{-}{NH_2} \) is the next strongest,
- \( OH^{-} \) follows,
- \( F^{-} \) is the weakest base (strongest acid).

4. **Final Order of Basic Strength**:
- Therefore, the order of decreasing basic strength is:
\[ \overset{-}{CH_3} > \overset{-}{NH_2} > OH^{-} > F^{-} \]

### Conclusion:
The final arrangement of the anions in decreasing order of their basic strength is:
\[ \overset{-}{CH_3} > \overset{-}{NH_2} > OH^{-} > F^{-} \]