Explanation:

- Water is indeed the most abundant molecule in cells, making up about 70% or more of the total cell mass. This high percentage is due to its crucial roles, including being a solvent, helping in chemical reactions, and regulating temperature.

- Lipids, while essential, do not make up the majority of cell mass. They are critical for forming cell membranes and storing energy.

- Nucleic acids, like DNA and RNA, are key for storing and transmitting genetic information, but they do not comprise a significant portion of cell mass compared to water.

- Proteins have diverse roles, including acting as enzymes, structural components, and signaling molecules. They are vital but not as abundant as water.

Option 1, Water, is correct.