Write the correct order of acidic strength of following compounds:
`(a)CH_(4)" "(b)NH_(3)`
`(c)H_(2)O" "(d)H-F`

Answer

To determine the correct order of acidic strength for the compounds \( CH_4 \), \( NH_3 \), \( H_2O \), and \( HF \), we will analyze the stability of their conjugate bases. The stability of the conjugate base is a key factor in determining the acidity of the corresponding acid.

### Step-by-Step Solution:

1. **Identify the Compounds:**
- (a) \( CH_4 \) (methane)
- (b) \( NH_3 \) (ammonia)
- (c) \( H_2O \) (water)
- (d) \( HF \) (hydrofluoric acid)

2. **Form the Conjugate Bases:**
- For \( CH_4 \): Remove \( H^+ \) to get \( CH_3^- \) (methyl anion).
- For \( NH_3 \): Remove \( H^+ \) to get \( NH_2^- \) (amide ion).
- For \( H_2O \): Remove \( H^+ \) to get \( OH^- \) (hydroxide ion).
- For \( HF \): Remove \( H^+ \) to get \( F^- \) (fluoride ion).

3. **Evaluate the Conjugate Bases:**
- The stability of the conjugate base is influenced by the electronegativity of the atom bearing the negative charge.
- The more electronegative the atom, the better it can stabilize the negative charge.

4. **Electronegativity Order:**
- Fluorine (F) > Oxygen (O) > Nitrogen (N) > Carbon (C)
- Thus, the order of stability of the conjugate bases is:
- \( F^- \) (most stable)
- \( OH^- \)
- \( NH_2^- \)
- \( CH_3^- \) (least stable)

5. **Determine the Order of Acidity:**
- The stronger the conjugate base, the weaker the corresponding acid.
- Therefore, the order of acidic strength from strongest to weakest is:
- \( HF \) > \( H_2O \) > \( NH_3 \) > \( CH_4 \)

### Final Order of Acidic Strength:
\[ HF > H_2O > NH_3 > CH_4 \]