Among the acids
1. `"HC"-="C"-"COOH"`
2. `"H"_(2)"C"="CH"-"COOH"`
3. `"CH"_(3)-"CH"_(2)-"COOH"`
The acidic strength follows the order

Options

A. `XltYltZ`
B. `XltZltY`
C. `YltXltZ`
D. `ZltYltX`

Answer

To determine the order of acidic strength among the given acids, we need to analyze the structure of each acid and the hybridization of the carbon atom adjacent to the carboxylic acid group (-COOH).

### Step-by-Step Solution:

1. **Identify the Structures**:
- The first acid is **HC≡C-COOH** (propyne-1-carboxylic acid).
- The second acid is **H2C=CH-COOH** (acrylic acid).
- The third acid is **CH3-CH2-COOH** (propanoic acid).

2. **Determine the Hybridization of the Alpha Carbon**:
- In **HC≡C-COOH**, the alpha carbon (the one directly attached to the -COOH group) is **sp hybridized** due to the triple bond.
- In **H2C=CH-COOH**, the alpha carbon is **sp² hybridized** due to the double bond.
- In **CH3-CH2-COOH**, the alpha carbon is **sp³ hybridized** as it is connected to single bonds only.

3. **Electronegativity Order**:
- The electronegativity of carbon increases with increasing s-character in hybridization:
- sp (50% s-character) > sp² (33% s-character) > sp³ (25% s-character).
- Therefore, the electronegativity order is: **sp > sp² > sp³**.

4. **Effect on Acidity**:
- A more electronegative carbon can better stabilize the negative charge that forms when the acid donates a proton (H⁺).
- Thus, the acidity increases with the increase in s-character of the hybridized carbon:
- The acid with the sp hybridized carbon (HC≡C-COOH) will be the strongest acid.
- The acid with the sp² hybridized carbon (H2C=CH-COOH) will be the second strongest.
- The acid with the sp³ hybridized carbon (CH3-CH2-COOH) will be the weakest.

5. **Conclusion**:
- The order of acidic strength is:
- **HC≡C-COOH > H2C=CH-COOH > CH3-CH2-COOH**.

### Final Answer:
The acidic strength follows the order: **HC≡C-COOH > H2C=CH-COOH > CH3-CH2-COOH**.

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