Explain the structure of ice.

(N/A) Ice has a highly ordered three-dimensional hydrogen-bonded structure as shown in the figure.
Examination of ice crystals with $X$-rays shows that each oxygen atom is surrounded tetrahedrally by four other oxygen atoms at a distance of $276 \text{ pm}$.
Hydrogen bonding gives ice a rather open-type structure with wide holes. These holes can hold some other molecules of appropriate size interstitially.