A molecule has a zero dipole moment if it is nonpolar. For a molecule to be nonpolar, two conditions must generally be met:

• The individual bond dipoles must be zero, or
• The individual bond dipoles must cancel each other out due to the molecule's symmetrical geometry.

Let's analyze each option:

A) ClF: This is a diatomic molecule with a bond between chlorine and fluorine. Since fluorine is more electronegative than chlorine, there is a significant difference in electronegativity, leading to a polar covalent bond and thus a net dipole moment. The molecule is linear.

B) PCl₃: Phosphorus trichloride has a central phosphorus atom bonded to three chlorine atoms and one lone pair of electrons. The presence of the lone pair gives PCl₃ a trigonal pyramidal geometry. Due to this asymmetrical geometry and the polar P-Cl bonds, the bond dipoles do not cancel out, resulting in a net dipole moment.

C) SiF₄: Silicon tetrafluoride has a central silicon atom bonded to four fluorine atoms. Silicon is in Group 14, and it forms four single bonds with fluorine atoms. There are no lone pairs on the central silicon atom. According to VSEPR theory, a molecule with four bonding pairs and no lone pairs around the central atom adopts a tetrahedral geometry. In a perfectly symmetrical tetrahedral molecule like SiF₄, even though the Si-F bonds are polar, their dipoles are oriented symmetrically in space and cancel each other out, leading to a net dipole moment of zero.

D) CFCl₃: Trichlorofluoromethane has a central carbon atom bonded to one fluorine atom and three chlorine atoms. This molecule has a tetrahedral geometry. However, since the surrounding atoms (F and Cl) are not identical, the individual bond dipoles (C-F and C-Cl) are different in magnitude. Therefore, these bond dipoles do not cancel each other out, resulting in a net dipole moment.

Correct Answer: (C)