Correct set of species with zero dipole moment is :
(i) `CO_(2) " " (ii) COCl_(2) " " (iii) CH_(2)Cl_(2) " " (iv) BCl_(3)`

Options

A. I and iv
B. ii and iv
C. iii and iv
D. I, iii and iv

Explanation

To determine which of the given species has a zero dipole moment, we need to analyze the molecular geometry and the electronegativity of the atoms involved in each molecule. A molecule will have a zero dipole moment if the individual bond dipoles cancel each other out due to the symmetry of the molecule.

### Step-by-Step Solution:

1. **Identify the Species**: The species we need to analyze are:
- (i) CO₂ (Carbon Dioxide)
- (ii) COCl₂ (Phosgene)
- (iii) CH₂Cl₂ (Dichloromethane)
- (iv) BCl₃ (Boron Trichloride)

2. **Analyze CO₂**:
- **Structure**: CO₂ is a linear molecule with the structure O=C=O.
- **Electronegativity**: Oxygen is more electronegative than carbon, creating bond dipoles directed towards the oxygen atoms.
- **Result**: The two dipoles are equal in magnitude and opposite in direction, thus they cancel each other out. **Dipole Moment = 0**.

3. **Analyze COCl₂**:
- **Structure**: COCl₂ has a bent structure (similar to H₂O) due to the presence of lone pairs on carbon.
- **Electronegativity**: Chlorine is more electronegative than carbon, leading to dipoles directed towards the chlorine atoms.
- **Result**: The dipoles do not cancel out completely due to the bent shape. **Dipole Moment ≠ 0**.

4. **Analyze CH₂Cl₂**:
- **Structure**: CH₂Cl₂ is also a tetrahedral molecule.
- **Electronegativity**: Chlorine is more electronegative than carbon, creating dipoles directed towards the chlorine atoms.
- **Result**: The dipoles do not cancel out due to the asymmetrical distribution of electronegative atoms. **Dipole Moment ≠ 0**.

5. **Analyze BCl₃**:
- **Structure**: BCl₃ has a trigonal planar structure.
- **Electronegativity**: Chlorine is more electronegative than boron, leading to dipoles directed towards the chlorine atoms.
- **Result**: The three dipoles are symmetrically arranged and cancel each other out. **Dipole Moment = 0**.

6. **Conclusion**: The species with zero dipole moment are CO₂ and BCl₃.

### Final Answer:
The correct set of species with zero dipole moment is: **(i) CO₂ and (iv) BCl₃**.