To determine which molecule has a zero dipole moment, we need to analyze the molecular geometry and the electronegativity of the atoms involved in the bonds. A molecule will have a zero dipole moment if it is symmetrical, meaning that the dipole moments of the individual bonds cancel each other out.
### Step-by-Step Solution:
1. **Identify the Molecules**: We need to evaluate the molecules NH3 (ammonia), H2O (water), and trans-1,2-dichloroethene (C2H2Cl2).
2. **Analyze NH3 (Ammonia)**:
- **Structure**: Nitrogen (N) has 5 valence electrons and forms three bonds with hydrogen (H), leaving one lone pair on nitrogen.
- **Geometry**: The geometry is tetrahedral due to the four electron pairs (3 bond pairs + 1 lone pair), but the shape is trigonal pyramidal.
- **Dipole Moment**: The molecule has a net dipole moment because of the lone pair on nitrogen, which creates an asymmetrical charge distribution. Therefore, NH3 has a dipole moment.
3. **Analyze H2O (Water)**:
- **Structure**: Oxygen (O) has 6 valence electrons and forms two bonds with hydrogen, leaving two lone pairs on oxygen.
- **Geometry**: The geometry is tetrahedral, but the shape is bent due to the two lone pairs.
- **Dipole Moment**: The bent shape leads to a net dipole moment because the polar bonds do not cancel out. Therefore, H2O has a dipole moment.
4. **Analyze Trans-1,2-Dichloroethene (C2H2Cl2)**:
- **Structure**: The molecule has a planar structure with two chlorine (Cl) atoms and two hydrogen (H) atoms.
- **Geometry**: The molecule is symmetrical, with the Cl atoms positioned opposite each other.
- **Dipole Moment**: The dipole moments of the C-Cl bonds cancel each other out due to the symmetry of the molecule. Therefore, trans-1,2-dichloroethene has a zero dipole moment.
5. **Conclusion**: Among the given options, trans-1,2-dichloroethene is the molecule that exhibits a zero dipole moment due to its symmetrical structure.
### Final Answer:
Zero dipole moment is present in trans-1,2-dichloroethene (C2H2Cl2).
