Explanation:
The dipole moment of a molecule is the measure of the polarity of the molecule, which is the result of the difference in electronegativity between the atoms in the molecule. If a molecule has a non-zero dipole moment, it means that the molecule is polar.

XF4 is a molecule with a central atom X and four fluorine atoms bonded to it. In order to determine if the molecule is polar, we need to consider the geometry of the molecule and the electronegativity of the atoms.

Geometry of XF4:

- X has four bonding pairs of electrons and no lone pairs of electrons.
- The shape of the molecule is tetrahedral with a bond angle of 109.5°.

Electronegativity of X and F:

- X is an element from the third period of the periodic table.
- F is an element from the second period of the periodic table.
- The electronegativity of X is 2.5, whereas the electronegativity of F is 3.98.

Based on the above information, we can conclude that the molecule XF4 is polar. This is because:

- The molecule has a tetrahedral shape with four identical polar bonds.
- The electronegativity difference between X and F is significant, resulting in a polar X-F bond.
- The polar X-F bonds are arranged symmetrically in the molecule, resulting in a non-zero dipole moment.

Therefore, the correct answer is option C, X is an element from the third period and the molecule XF4 is polar.