Which statement is true about a base when it reacts with another substance?
a. it receives a hydrogen ion.
b. it receives a hydroxide ion.
c. it donates a hydrogen ion.
d. it donates a hydroxide ion.

A. It receives a hydrogen ion.

Explanation:

The Bronsted lowry theory of acids and bases solves this problem. The theory states that;

Any compound that can transfer a proton to any other compound is an acid, and the compound that accepts the proton is a base. A proton is a nuclear particle with a unit positive electrical charge; it is represented by the symbol H+ because it constitutes the nucleus of a hydrogen atom.

So among the options, the option that says a base receives a hydrogen ion is the right answer which is option A.

Take the following reaction for example:

HCl  + NH₃    ⇌  NH₄⁺  +  Cl⁻

Hydrochloric acid (HCl) is the Brønsted-Lowry acid because it donates a hydrogen ion. Ammonia (NH3) is the Brønsted-Lowry base because it accepts the hydrogen ion.

explanation: it gains negative electrons, therefore becoming negatively charged. as charge cannot be created, nor destroyed, only transferred, this leaves the wool positive. now that they have opposite charges, the two items attract.