Answer:
H2O / H+
Step-by-step explanation:
In alkene hydration, water, being a very weak acid, with insufficient proton concentration, does not have the capacity to initiate the electrophilic addition reaction. An acid must be added to the medium for the reaction to take place.
The mechanism proceeds with the formation of a carbocation after adding the proton to the double bond. Alkene hydration is Markovnikov, that is, the proton is added to the less substituted carbon of the alkene.