Which statement describes polar molecules?

• A. They have a slightly positive end and a slightly negative end
• B. They have no charges
• C. They form nonpolar covalent bonds
• D. They move through the membrane by diffusion alone

Answer: (A)

Polar molecules have an unequal distribution of electric charge, producing partial charges on different parts of the molecule. The more electronegative atom pulls shared electrons closer, creating a slight negative charge near that atom, while the other end becomes slightly positive. Water is a classic example: the oxygen end is a bit negative and the hydrogen ends are a bit positive, giving the molecule a dipole.

This is why describing polar molecules as having a slightly positive end and a slightly negative end is accurate—they carry a dipole moment due to uneven electron sharing. The other statements don’t capture this feature: having no charges would describe nonpolar molecules; forming nonpolar covalent bonds leads to little or no charge separation; diffusion through a membrane is about membrane permeability, not the intrinsic definition of polarity.