A molecule is polar if it has a net dipole moment. This occurs when there are polar bonds and the molecular geometry is such that the bond dipoles do not cancel each other out. To determine polarity, we need to consider both the bond polarity and the molecular geometry.

SF₄: Sulfur has 6 valence electrons. In SF₄, sulfur forms 4 single bonds with fluorine atoms and has one lone pair of electrons. The steric number is 4 (bonds) + 1 (lone pair) = 5. According to VSEPR theory, this corresponds to a trigonal bipyramidal electron geometry. The lone pair occupies an equatorial position to minimize repulsion, resulting in a see-saw molecular geometry. Due to the presence of the lone pair and the asymmetric see-saw shape, the bond dipoles do not cancel out, making SF₄ a polar molecule.

• A) SiF₄: Silicon has 4 valence electrons. In SiF₄, silicon forms 4 single bonds with fluorine atoms and has no lone pairs. The steric number is 4. This results in a tetrahedral molecular geometry. All Si-F bonds are polar, but due to the symmetrical tetrahedral structure, the bond dipoles cancel each other out, making SiF₄ a non-polar molecule.

• B) XeF₄: Xenon has 8 valence electrons. In XeF₄, xenon forms 4 single bonds with fluorine atoms and has two lone pairs of electrons. The steric number is 4 (bonds) + 2 (lone pairs) = 6. This corresponds to an octahedral electron geometry. The two lone pairs occupy opposite positions (axial) to minimize repulsion, resulting in a square planar molecular geometry. Due to the symmetrical square planar structure, the bond dipoles cancel each other out, making XeF₄ a non-polar molecule.

• C) BF₃: Boron has 3 valence electrons. In BF₃, boron forms 3 single bonds with fluorine atoms and has no lone pairs. The steric number is 3. This results in a trigonal planar molecular geometry. All B-F bonds are polar, but due to the symmetrical trigonal planar structure, the bond dipoles cancel each other out, making BF₃ a non-polar molecule.

Correct Answer: (D)