Which of the following best describes inorganic compounds?

Inorganic compounds are defined as chemical compounds that do not contain carbon-hydrogen (C-H) bonds. The correct choice highlights that inorganic compounds typically include substances such as acids, bases, and salts that do not have carbon in their structure.

This classification is important in various fields, including environmental science and water treatment, as many inorganic compounds play a significant role in the characteristics and quality of water. For instance, salts can influence the conductivity of water, while acids and bases can affect pH levels, making it vital for operators to understand their properties and implications in water treatment processes.

The other options, while related to different types of substances, do not accurately encapsulate the definition of inorganic compounds. Compounds containing carbon, pure metals, and plastic materials can include organic compounds or materials that fall outside the realm of inorganic chemistry. Thus, the emphasis on acids, bases, and salts lacking carbon specifically points to the essential nature of inorganic compounds in various applications, particularly in the context of drinking water treatment.