Which of the following is the correct order of bond-angle ?

Options

A. `NH_(3) lt CH_(4) lt C_(2)H_(2) lt H_(2)O`
B. `C_(2)H_(2)lt NH_(3) lt H_(2)Olt CH_(4)`
C. `NH_(3) lt H_(2)Olt CH_(4) lt C_(2)H_(2)`
D. `H_(2)Olt NH_(3) lt CH_(4) lt C_(2)H_(2)`

Answer

To determine the correct order of bond angles for the given molecules (water, ammonia, methane, and ethyne), we can follow these steps:

### Step 1: Identify the Molecular Structures
- **Water (H2O)**: Oxygen has 6 valence electrons, with 2 lone pairs and 2 bond pairs.
- **Ammonia (NH3)**: Nitrogen has 5 valence electrons, with 1 lone pair and 3 bond pairs.
- **Methane (CH4)**: Carbon has 4 valence electrons, with 0 lone pairs and 4 bond pairs, forming a tetrahedral shape.
- **Ethyne (C2H2)**: This molecule has a linear structure with a triple bond between the two carbon atoms and 2 hydrogen atoms.

### Step 2: Determine the Bond Angles
- **Ethyne (C2H2)**: The bond angle is 180° because it is linear.
- **Methane (CH4)**: The bond angle is approximately 109.5° because it is tetrahedral.
- **Ammonia (NH3)**: The bond angle is approximately 107° due to the presence of one lone pair, which slightly reduces the angle from the ideal tetrahedral angle.
- **Water (H2O)**: The bond angle is approximately 104.5° because it has two lone pairs, which exert greater repulsion and reduce the bond angle further.

### Step 3: Arrange the Bond Angles in Order
Based on the bond angles calculated:
1. Ethyne (C2H2) - 180°
2. Methane (CH4) - 109.5°
3. Ammonia (NH3) - 107°
4. Water (H2O) - 104.5°

### Final Order of Bond Angles
Thus, the correct order of bond angles from largest to smallest is:
**C2H2 > CH4 > NH3 > H2O**

### Answer
The correct order of bond angles is:
**C2H2 > CH4 > NH3 > H2O**

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