Which of the following is a common example of a reactive chemical?

Sodium is a well-known example of a reactive chemical due to its highly reactive nature, particularly when it comes into contact with water and air. When sodium reacts with water, it generates hydrogen gas and produces sodium hydroxide, leading to an exothermic reaction that can cause fires or explosions. This characteristic makes sodium essential to handle with precautions in environments where reactive substances may be present.

In contrast, water is relatively stable and does not exhibit significant reactivity under normal conditions. Ammonia, while it can be reactive, is generally more stable and primarily acts as a base and a reagent in various chemical reactions. Ethanol is also a more stable organic compound that is less likely to react dangerously under standard conditions. Thus, sodium's vigorous reactions with moisture and other elements firmly categorize it as a common reactive chemical in safety contexts.