What property of water allows it to form hydrogen bonds?

The property of water that allows it to form hydrogen bonds is its polar nature. Water molecules are polar because of the uneven distribution of electron density, with the oxygen atom being more electronegative than the hydrogen atoms. This results in a partial negative charge on the oxygen and a partial positive charge on the hydrogens.

Because of this polarity, water molecules are attracted to each other, as the positive side of one molecule will be attracted to the negative side of another. This attraction creates hydrogen bonds, which are relatively weak compared to covalent or ionic bonds but are significant in number, giving water many of its unique properties, such as its high surface tension and its ability to dissolve various substances effectively.

The other options do not lead to the formation of hydrogen bonds. A low pH value would indicate high acidity, which does not directly relate to hydrogen bond formation. A nonpolar nature would mean there is no significant charge separation, preventing bonds like hydrogen bonds from forming. While high density is a characteristic of water, it is not the reason for the formation of hydrogen bonds; rather, it is a consequence of the hydrogen bonding that occurs between water molecules.