Here's why:

* Brønsted-Lowry Acid-Base Theory: This theory defines acids as proton donors and bases as proton acceptors.

* Proton: A proton is a hydrogen ion (H+).

So, when a base reacts with an acid, it accepts a proton from the acid, forming a new compound.

Example:

* Ammonia (NH3) is a base. It can accept a proton from water (H2O) to form the ammonium ion (NH4+).

NH3 + H2O ⇌ NH4+ + OH-

In this reaction, ammonia accepts a proton from water, making it a base.