Of the molecules Cl2C=Cl2, IF3, and SF6?

The shapes of the three molecules and the dipole moments of the bonds are shown below.

The dipole moment of a molecule is the vector sum of dipole moments of all the bonds in the molecule.

In Cl₂C=CCl₂, the dipole moments of the four C-Cl bonds cancel each other. Hence, the dipole moment of Cl₂C=CCl₂ molecule is zero and thus the molecule does not have a net dipole moment.

In IF₃, the dipole moments of the three I-F bonds cannot cancel each other. Hence, the dipole moment of IF₃ molecule is non-zero and thus the molecule has a net dipole moment.

In SF₆, the dipole moments of the six S-F bonds cancel each other. Hence, the dipole moment of SF₆ molecule is zero and thus the molecular does not have a net dipole moment.