Which of the following is NOT a unique property of water?

The unique property of water that is not included in the affirmative list is the density of gas. Water exhibits several distinctive properties that arise from its molecular structure and hydrogen bonding. Cohesion refers to the attractive forces between water molecules, allowing them to stick together, which is crucial for processes like water transport in plants. Polarity means that water molecules have a partial positive charge on one side and a partial negative charge on the other, leading to water's ability to dissolve many substances, making it an excellent solvent. Adhesion, on the other hand, describes the attraction between water molecules and other substances, contributing to phenomena such as capillary action.

In contrast, the statement about the density of gas does not reflect a unique property of water itself but rather refers to physical characteristics of gases in general. Water does not stand out from other substances in terms of gas density; thus, it is appropriate to identify this choice as the one that does not align with the unique properties associated specifically with water.