The correct answer is option 3: Hydrogen-bonding in ice gives an open type structure with interstitial holes.

To understand why ice floats on water, we need to consider the structure of ice and water.

In water, the molecules are packed closely together, with hydrogen bonding occurring between neighboring water molecules. These hydrogen bonds give water its unique properties, such as high boiling and melting points, as well as its ability to dissolve many substances.

In ice, however, the water molecules form a crystalline lattice structure, which is held together by hydrogen bonds. This results in an open, 3-dimensional structure with interstitial holes or empty spaces.

The presence of these interstitial holes in ice makes its density lower than that of liquid water. When ice forms, the water molecules spread out and form a lattice, which increases the volume and decreases the density.

As a result, ice is less dense than water, which causes it to float on the water surface. If ice were denser than water, it would sink. This phenomenon of ice floating on water is crucial for the survival of aquatic ecosystems, as it allows insulation and prevents bodies of water from freezing solid.

Therefore, option 3 correctly explains that the open structure of ice, caused