Here's why:

* Bases produce hydroxide ions (OH-) in solution.

* Acids produce hydrogen ions (H+) in solution.

When a base and an acid react, the hydrogen ions from the acid combine with the hydroxide ions from the base to form water (H2O). The remaining ions from the acid and base then combine to form a salt.

For example:

* Sodium hydroxide (NaOH) is a base and produces Na+ and OH- ions in solution.

* Hydrochloric acid (HCl) is an acid and produces H+ and Cl- ions in solution.

When NaOH and HCl react:

* H+ + OH- → H2O (water)

* Na+ + Cl- → NaCl (salt, specifically sodium chloride)

This is a classic example of a neutralization reaction where the acid and base neutralize each other to form a salt and water.