Concept: Intermolecular Forces

Intermolecular forces are attractive forces that exist between molecules. These forces are responsible for many physical properties of substances, including melting point, boiling point, and solubility. Water molecules (H₂O) are polar and can form strong intermolecular forces.

Why (C) is correct:

Ice is solid water. Water molecules are highly polar due to the significant electronegativity difference between oxygen and hydrogen. This polarity leads to the formation of strong hydrogen bonds between water molecules. When two ice blocks are pressed together, the water molecules on their surfaces can form new hydrogen bonds with each other, effectively 'freezing' them together. This phenomenon is known as regelation, where pressure causes a slight melting, and then the water refreezes, forming new hydrogen bonds.

Option Analysis:

• A) London forces: These are weak, temporary attractive forces that occur between all molecules, but they are particularly significant for nonpolar molecules. While present in ice, they are not the primary force responsible for holding ice blocks together.
• B) Dipole-dipole interaction: These forces occur between polar molecules. Hydrogen bonding is a special, stronger type of dipole-dipole interaction involving hydrogen bonded to a highly electronegative atom (like O, N, or F). Therefore, while dipole-dipole interactions exist, hydrogen bonding is the more specific and dominant force here.
• D) Ionic forces: These are strong electrostatic forces between oppositely charged ions. Ice is composed of neutral water molecules, not ions, so ionic forces are not involved.

Correct Answer: (C)