Concept: Molecular polarity depends on two main factors: the polarity of individual bonds and the molecular geometry. 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. If the bond dipoles cancel due to symmetrical geometry, the molecule is non-polar, even if individual bonds are polar.

Why (C) PCl₃ is correct:

• PCl₃: Phosphorus trichloride has a central phosphorus atom bonded to three chlorine atoms and one lone pair of electrons. The steric number is 4 (3 bond pairs + 1 lone pair), leading to a trigonal pyramidal geometry. The P-Cl bonds are polar due to the difference in electronegativity between P and Cl. Because of the trigonal pyramidal geometry and the presence of the lone pair, the individual bond dipoles do not cancel out, resulting in a net dipole moment. Therefore, PCl₃ is a polar molecule.

Option Analysis:

• A) BF₃: Boron trifluoride has a central boron atom bonded to three fluorine atoms with no lone pairs. Its geometry is trigonal planar. Although the B-F bonds are polar, the symmetrical trigonal planar arrangement causes the bond dipoles to cancel each other out, making BF₃ a non-polar molecule.
• B) XeO₄: Xenon tetroxide has a central xenon atom bonded to four oxygen atoms with no lone pairs. Its geometry is tetrahedral. The Xe-O bonds are polar, but the symmetrical tetrahedral arrangement causes the bond dipoles to cancel each other out, making XeO₄ a non-polar molecule.
• D) CO₂: Carbon dioxide has a central carbon atom double-bonded to two oxygen atoms with no lone pairs on the central atom. Its geometry is linear. Although the C=O bonds are polar, the symmetrical linear arrangement causes the bond dipoles to cancel each other out, making CO₂ a non-polar molecule.

Correct Answer: (C)