According to one acid-base theory, the h2o(l) molecules act as

both an acid and base

Explanation: By Bronsted-Lowery acid base theory: proton Donor is acid and proton Acceptor is base.

Here H2O by donating the proton acts as acid.

H2O > H^+ + OH^-

And by accepting the proton acts as base

H2O + H+ > H3O+

the answer is:  

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