Which term refers to the unequal distribution of electrons?

• A. Isotonic
• B. Adhesion
• C. Endosymbiotic theory
• D. Polarity

Answer: (D)

Polarity is when electrons are not shared equally in a molecule. In covalent bonds between atoms with different electronegativities, the more electronegative atom pulls the shared electrons closer, giving it a partial negative charge while the other atom ends up with a partial positive charge. This uneven distribution creates a dipole, or a molecule with charged regions. Water is a key example: oxygen attracts electrons more strongly than hydrogen, so the oxygen end is slightly negative and the hydrogens are slightly positive, enabling hydrogen bonding and many of water’s properties that support life.

The other terms describe different ideas: isotonic refers to equal solute concentrations across a membrane, adhesion is the attraction between unlike molecules, and the endosymbiotic theory explains the origin of organelles like mitochondria and chloroplasts. Polarity specifically captures the unequal distribution of electrons.