Among the following, the most polar molecule is :

Options

A. `AlCl_3`
B. `"CC"l_4`
C. `SeCl_6`
D. `AsCl_3`

Explanation

To determine which of the given molecules is the most polar, we will analyze each option based on their molecular geometry and the presence of dipole moments.

### Step-by-Step Solution:

1. **Identify the Given Molecules:**
The options provided are AlCl3, CCl4, SeCl6, and AsCl3.

2. **Analyze AlCl3 (Aluminum Chloride):**
- Aluminum (Al) has 3 valence electrons and forms 3 bonds with chlorine (Cl).
- The molecular geometry of AlCl3 is trigonal planar.
- In a trigonal planar structure, the dipole moments of the bonds cancel out due to symmetry.
- **Conclusion:** AlCl3 is a non-polar molecule.

3. **Analyze CCl4 (Carbon Tetrachloride):**
- Carbon (C) has 4 valence electrons and forms 4 bonds with chlorine.
- The molecular geometry of CCl4 is tetrahedral.
- Similar to AlCl3, the dipole moments in CCl4 cancel out due to its symmetrical shape.
- **Conclusion:** CCl4 is a non-polar molecule.

4. **Analyze SeCl6 (Selenium Hexachloride):**
- Selenium (Se) has 6 valence electrons and forms 6 bonds with chlorine.
- The molecular geometry of SeCl6 is octahedral.
- In an octahedral structure, the dipole moments also cancel out due to symmetry.
- **Conclusion:** SeCl6 is a non-polar molecule.

5. **Analyze AsCl3 (Arsenic Trichloride):**
- Arsenic (As) has 5 valence electrons and forms 3 bonds with chlorine, leaving one lone pair.
- The molecular geometry of AsCl3 is trigonal pyramidal due to the presence of the lone pair.
- The lone pair creates an asymmetrical distribution of charge, resulting in a net dipole moment.
- **Conclusion:** AsCl3 is a polar molecule.

6. **Final Conclusion:**
Among the given options, the only polar molecule is AsCl3. Therefore, it is the most polar molecule among the options provided.

### Answer:
The most polar molecule is **AsCl3**.