This reaction is called a neutralization reaction because the acid and base react to form salt and water. The hydrogen ions (H⁺) from the acid combine with the hydroxide ions (OH⁻) from the alkali to form water (H₂O), and the remaining ions form a salt.

Here's a simple example:

Hydrochloric acid (HCl) + Sodium hydroxide (NaOH) → Sodium chloride (NaCl) + Water (H₂O)

In this reaction, the hydrogen ions from HCl combine with the hydroxide ions from NaOH to form water. The remaining ions, sodium (Na⁺) and chloride (Cl⁻), form the salt sodium chloride.

Note: Not all acid-base reactions produce hydrogen gas. For example, the reaction between a strong acid like hydrochloric acid and a weak base like ammonia will not produce hydrogen gas.