Water's unique properties, including its high heat capacity, high density, high boiling point and a solid phase that is less dense than its liquid phase, can best be attributed to:
a) its formula, h2o.
b) the covalent oxygen-hydrogen bonds in the molecule.
c) the shape of the molecule.
d) the polarity of the molecule and hydrogen bonding between the molecules.

Option (D) is the correct answer.

Explanation:

As the chemical formula of water is and due to the difference in electronegativity of hydrogen and oxygen atom there is formation of partial positive charge on hydrogen and partial negative charge on oxygen atom.

As a result, polarity arises on water molecule.

Also, there exists hydrogen bonding between molecules of water which is also responsible for providing unique properties to water.

Thus, we can conclude that water's unique properties, including its high heat capacity, high density, high boiling point and a solid phase that is less dense than its liquid phase, can best be attributed to the polarity of the molecule and hydrogen bonding between the molecules.