The conjugate base of H2O is OH– (hydroxide ion).
When water (H2O) donates a proton (H+), it forms the hydroxide ion (OH–). This process can be represented by the following chemical equation:
H2O → H+ + OH–
In this reaction, water acts as an acid by donating a proton, and the resulting hydroxide ion is its conjugate base. The concept of conjugate acids and bases is fundamental in understanding acid-base reactions in chemistry.