Which of the following is polar?

• A. NF₃
• B. BF₃
• C. SF₄
• D. SiF₄

To determine which of the given molecules is polar, we need to consider their molecular geometry and the electronegativity of the atoms involved.

Analyzing Each Option

• NF₃ (Nitrogen Trifluoride): This molecule has a trigonal pyramidal shape due to the presence of a lone pair on nitrogen. The difference in electronegativity between nitrogen and fluorine creates a dipole moment, making NF₃ polar.
• BF₃ (Boron Trifluoride): BF₃ has a trigonal planar geometry and is symmetrical. The dipoles cancel each other out, resulting in a nonpolar molecule.
• SF₄ (Sulfur Tetrafluoride): SF₄ has a seesaw shape, which leads to an uneven distribution of charge. This asymmetry makes SF₄ polar.
• SiF₄ (Silicon Tetrafluoride): SiF₄ has a tetrahedral structure, and due to its symmetry, the dipoles cancel out, making it nonpolar.

Final Assessment

Among the options, both NF₃ and SF₄ are polar molecules. However, if you need to choose just one, NF₃ is often highlighted as a classic example of a polar molecule.