What is a reversible reaction? Provide an example.

A reversible reaction is a chemical reaction where the products can react to form the original reactants. An example is the thermal decomposition of ammonium chloride, which can break down into ammonia and hydrogen chloride gas, and can also reform ammonium chloride when the gases react.

This question tests the student's understandingof the definition of reversible reactions and their ability to provide a relevant example. It assesses recall and understandingof key concepts in reversible reactions.