What type of reaction occurs when an acid and a base combine to form water and a salt?

When an acid and a base combine, the primary result is the formation of water and a salt, which characterizes a neutralization reaction. In a neutralization reaction, the H⁺ ions from the acid react with the OH⁻ ions from the base to produce water (H₂O). The remaining anions from the acid and cations from the base form a salt, completing the reaction.

Neutralization reactions are fundamental in acid-base chemistry and are crucial in various applications, including titrations in analytical chemistry, buffering agents in biological systems, and everyday applications like mixing baking soda (a base) with vinegar (an acid) for cleaning or cooking purposes.

The other types of reactions listed—synthesis, decomposition, and redox—do not describe the interaction between an acid and a base accurately. Synthesis involves combining simpler substances into a more complex compound, decomposition involves breaking down a compound into simpler parts, and redox reactions entail the transfer of electrons between chemical species, which is not the primary process occurring in acid-base neutralization.