1. Principle used

A molecule has a permanent dipole moment if the vector sum of all bond dipoles is non-zero.

So we must check, in each option, whether all four molecules are polar at room temperature.

2. Option A: $SO_2$, $C_6H_5Cl$, $H_2Se$, $BrF_5$

• $SO_2$: bent shape due to lone pair on S. $\mu \neq 0$ So it is polar.

• $C_6H_5Cl$ (chlorobenzene): the $C-Cl$ bond gives a net molecular dipole; molecule is not symmetrically cancelling to zero. Hence polar.

• $H_2Se$: like $H_2O/H_2S$, it has a bent structure. Therefore bond dipoles do not cancel. Polar.

• $BrF_5$: square pyramidal geometry. This shape is unsymmetrical, so dipoles do not cancel. Polar.

Thus, all four are polar.

✅ Option A is correct.

3. Option B: $BeCl_2$, $CO_2$, $BCl_3$, $CHCl_3$

• $BeCl_2$: linear $Cl-Be-Cl$ Equal bond dipoles cancel. Non-polar.

• $CO_2$: linear, symmetric. Non-polar.

• $BCl_3$: trigonal planar, symmetric. Non-polar.

• $CHCl_3$: tetrahedral, unsymmetrical. Polar.

Since not all four are polar, this option is not correct.

❌ Option B is incorrect.

4. Option C: $NO_2$, $NH_3$, $POCl_3$, $CH_3Cl$

• $NO_2$: bent molecule. Hence polar.

• $NH_3$: trigonal pyramidal due to lone pair on N. Polar.

• $POCl_3$: tetrahedral arrangement around P with one $P=O$ and three $P-Cl$ bonds; substituents are not identical, so dipoles do not cancel. Polar.

• $CH_3Cl$: tetrahedral but unsymmetrical because one Cl and three H. Polar.

Thus, all four are polar.

✅ Option C is correct.

5. Option D: $BF_3$, $O_3$, $SF_6$, $XeF_6$

• $BF_3$: trigonal planar and symmetric. Non-polar.

• $O_3$: bent, polar.

• $SF_6$: octahedral and symmetric. Non-polar.

• $XeF_6$: distorted octahedral / monocapped octahedron, generally polar.

Since $BF_3$ and $SF_6$ are non-polar, not all four are polar.

❌ Option D is incorrect.

6. Final conclusion

The options in which all four molecules possess permanent dipole moment at room temperature are: $\boxed{A,\ C}$

7. Comparison with stored correct answer

Stored correct answer: A, C

My derived answer: A, C

They match.