Concept: Hydrogen bonding is a special type of dipole-dipole interaction that occurs between a hydrogen atom covalently bonded to a highly electronegative atom (like O, N, or F) and another highly electronegative atom with a lone pair of electrons.

Why (D) is correct:

A water molecule ($H_{2}O$) has two hydrogen atoms and two lone pairs of electrons on the oxygen atom. Each hydrogen atom can form one hydrogen bond with an oxygen atom of an adjacent water molecule. Additionally, the oxygen atom, due to its two lone pairs, can accept two hydrogen bonds from the hydrogen atoms of two other adjacent water molecules. Therefore, one water molecule can participate in a total of four hydrogen bonds: two through its hydrogen atoms and two through its oxygen atom's lone pairs.

• Option A (1): Incorrect. A water molecule can form more than one hydrogen bond.
• Option B (2): Incorrect. While it has two H atoms, its oxygen can also accept two H-bonds.
• Option C (3): Incorrect. The oxygen atom has two lone pairs, allowing it to accept two H-bonds, in addition to the two H-bonds formed by its hydrogen atoms.
• Option D (4): Correct. Two H-bonds are formed by the two hydrogen atoms of the water molecule, and two H-bonds are accepted by the two lone pairs on the oxygen atom.

Correct Answer: (D)