The conjugate acid of H2O is H3O+.
When water (H2O) acts as a base, it can accept a proton (H+) to form hydronium ion (H3O+). This is a key concept in acid-base chemistry, where an acid is defined as a proton donor and a base as a proton acceptor. In this case, water is accepting a proton, transforming into its conjugate acid, H3O+.
The other options do not represent the correct conjugate acid of water. OH– is the conjugate base of water, while H+ is just a proton and not the result of water accepting a proton. H2O itself is neither a base nor acid in this context but can function as both depending on the chemical environment.