In an ice crystal, each water molecule is hydrogen bonded to ______ neighbouring molecules.

Determine the number of neighbouring water molecules hydrogen-bonded to each water molecule in an ice crystal.

Structure of ice.

In ice, water molecules arrange in a tetrahedral crystal structure. Each oxygen atom is at the centre of a tetrahedron.

Hydrogen bonding in ice.

Each water molecule forms four hydrogen bonds with its neighbours:

Two hydrogen bonds where the molecule acts as a donor (through its two O-H bonds).

Two hydrogen bonds where the molecule acts as an acceptor (through its two lone pairs on oxygen).

This gives each water molecule exactly 4 hydrogen-bonded neighbours, consistent with the tetrahedral arrangement in the ice crystal.

The correct answer is 4.