text: This substance can contain structures called Zundel cations and Eigen ["AY-gen"] cations.
full_question: This substance can contain structures called Zundel cations and Eigen ["AY-gen"] cations. The Grotthuss mechanism attempts to explain this substance's conductivity. This substance forms a "cage" around methane in a methane clathrate. This substance's solid-liquid equilibrium line has a negative slope on a P-T diagram, and it has a high boiling point because each molecule of this compound forms four hydrogen bonds. This molecule has a bent geometry with two lone pairs. The boiling point and melting point of this compound define the Celsius scale. This compound is more dense as a liquid than as a solid. For 10 points, name this universal solvent, with formula of H2O.
first_sentence: This substance can contain structures called Zundel cations and Eigen ["AY-gen"] cations.
raw_answer: water [or H2O before mention; or ice]