The molecule having smallest bond angle is

Options

A. `NCI_(3)`
B. `AsCI_(3)`
C. `SbCI_(3)`
D. PCI_(3)`

Answer

To determine which molecule has the smallest bond angle among the given options (NCl3, AsCl3, SbCl3, and PCl3), we will analyze the hybridization, geometry, and the electronegativity of the central atom in each molecule.

### Step-by-Step Solution:

1. **Identify the Central Atom and Valence Electrons**:
- For each molecule, identify the central atom and count its valence electrons.
- **NCl3**: Nitrogen (N) has 5 valence electrons.
- **AsCl3**: Arsenic (As) has 5 valence electrons.
- **SbCl3**: Antimony (Sb) has 5 valence electrons.
- **PCl3**: Phosphorus (P) has 5 valence electrons.

2. **Determine the Steric Number**:
- The steric number is calculated as the number of sigma bonds plus the number of lone pairs.
- For all molecules (NCl3, AsCl3, SbCl3, PCl3), there are 3 Cl atoms bonded to the central atom and 1 lone pair.
- Steric number = 3 (sigma bonds) + 1 (lone pair) = 4.

3. **Determine Hybridization**:
- With a steric number of 4, the hybridization for all the molecules is **sp³**.

4. **Determine Geometry and Shape**:
- All molecules have a tetrahedral geometry due to sp³ hybridization.
- However, the presence of one lone pair makes the shape of each molecule **trigonal pyramidal**.

5. **Consider Electronegativity**:
- The bond angle is influenced by the electronegativity of the central atom. Higher electronegativity generally leads to larger bond angles.
- The electronegativity trend in the nitrogen group (group 15) is as follows: N > P > As > Sb.
- Therefore, nitrogen has the highest electronegativity and antimony has the lowest.

6. **Compare Bond Angles**:
- Since all molecules have the same hybridization and geometry, the bond angle will be inversely related to the electronegativity of the central atom.
- Thus, the bond angle will be smallest for the molecule with the least electronegative central atom, which is **SbCl3**.

### Final Answer:
The molecule with the smallest bond angle is **SbCl3** (option C).