Mercuric oxide (HgO) is heated and forms liquid mercury (Hg) and oxygen (O2) gas. How would you characterize this reaction?

Decomposition reaction.

Explanation:

Decomposition reaction -

It is the type of reaction, where a single entity breaks down into various products under the influence of some external factors, like heat and sunlight, is referred to as a decomposition reaction.

From the question,

The reaction is -

2 HgO → 2 Hg + O₂

Hence,

A single compound HgO breaks down to two entities, i. e., Hg and O₂.