Order of acidity of `H_(2)O, NH_(3)` and acetylene is :

Options

A. `NH_(3) gt CH-=CH gt H_(2)O`
B. `H_(2)O gt NH_(3) gt CH-=CH`
C. `H_(2)O gt CH-=CHgt NH_(3)`
D. `NH_(3)gt H_(2)O gt CH-=CH`

Explanation

To determine the order of acidity of \( H_2O \), \( NH_3 \), and acetylene (\( HC \equiv CH \)), we need to analyze the ability of each compound to donate a proton (\( H^+ \)) and the stability of the resulting conjugate base.

### Step-by-Step Solution:

1. **Understanding Acidity**:
- Acidity is defined by the ability of a substance to donate a proton (\( H^+ \)). The more readily a compound donates a proton, the stronger the acid.

2. **Identify the Compounds**:
- We have three compounds: water (\( H_2O \)), ammonia (\( NH_3 \)), and acetylene (\( HC \equiv CH \)).

3. **Conjugate Bases Formation**:
- When \( H_2O \) donates a proton, it forms \( OH^- \).
- When \( NH_3 \) donates a proton, it forms \( NH_2^- \).
- When acetylene donates a proton, it forms \( HC \equiv C^- \).

4. **Stability of Conjugate Bases**:
- The stability of the conjugate base is crucial in determining acidity. A more stable conjugate base corresponds to a stronger acid.
- \( OH^- \) (from water) is relatively stable due to the electronegativity of oxygen.
- \( NH_2^- \) (from ammonia) is less stable than \( OH^- \) because nitrogen is less electronegative than oxygen.
- \( HC \equiv C^- \) (from acetylene) is the least stable because the negative charge is on a carbon atom that is sp-hybridized, which can hold the negative charge but is less stable compared to the other two.

5. **Comparing Acidity**:
- Since \( OH^- \) is the most stable conjugate base, \( H_2O \) is the strongest acid.
- Next, \( NH_2^- \) is more stable than \( HC \equiv C^- \), making ammonia a stronger acid than acetylene.
- Therefore, the order of acidity is:
\[ H_2O > NH_3 > HC \equiv CH \]

6. **Final Order**:
- The final order of acidity is \( H_2O > HC \equiv CH > NH_3 \).