Which of the following is NOT a type of microorganism?

Microorganisms are defined as microscopic organisms that can only be seen with the aid of a microscope. They include a diverse group, such as viruses, bacteria, and fungi, each having unique structures and characteristics.

Among the listed options, gas does not fit the criteria for microorganisms. Gas is a state of matter and does not possess the biological characteristics necessary to be classified as a living organism. It lacks cellular structure and the ability to reproduce independently, which are fundamental traits of microorganisms.

In contrast, viruses are infectious agents that need a host cell to replicate; bacteria are unicellular organisms that can live independently; and fungi consist of multicellular or unicellular organisms that can reproduce and obtain nutrients in various ways. Thus, identifying gas as something that does not fit the definition of microorganisms highlights the specific characteristics that define this category of life.