What class of chemical compounds must contain hydrogen?

Organic compounds are defined by their carbon-based structure, and a fundamental characteristic of these compounds is that they contain hydrogen. The presence of hydrogen, along with carbon, allows for a variety of structures and functions within organic chemistry, including the formation of hydrocarbons and functional groups that are essential for biological processes.

In contrast, inorganic compounds can exist without hydrogen and may consist of a variety of elements, including metals and non-metals. Salts, which are typically composed of metal cations and non-metal anions, do not need to include hydrogen in their composition. Similarly, minerals, which are naturally occurring inorganic substances, can also lack hydrogen in their structure.

Therefore, the necessity of hydrogen in organic compounds distinguishes them clearly from these other categories, making them unique and fundamental to the study of life and biological systems.