Three diagnostic characteristics of an acid are:

three diagnostic characteristics of a base are:

An acid:

According to Arrhenius Theory, is a substance that interacts with water to produce excess hydrogen ion in an aqeous solution. The Bronsted - Lowry Theory defines an acid as a proton donor. The Lewis Theory states that an acid is an electron pair acceptor.

A base:

Arrhenius defined a base as a substance which interacts with water to yield excess hydroxide ions in an aqeous solution. Bronsted-Lowry defined a base as a proton acceptor. The Lewis Theory described a base as an electron pair donor.