According to one acid base theory a base is an 1, h2 acceptor 2, h2 donor 3, h + acceptor 4, h + donor

3, H⁺ acceptor

Explanation:

Let's consider Bronsted-Lowry acid-base theory.

According to this theory, an acid is a substance that donates H⁺ ions. For example, HCl is an acid.

HCl + H₂O = Cl⁻ + H₃O⁺

Cl⁻ is the conjugate base of HCl.

According to this theory, a base is a substance that accepts H⁺ ions. For example, NH₃ is a base.

NH₃ + H₂O = NH₄⁺ + OH⁻

NH₄⁺ is the conjugate acid of NH₃.