Which of the following are considered micronutrients?

Micronutrients are essential elements that organisms require in small quantities for proper physiological functioning. Trace elements such as iron and zinc fall into this category because they play critical roles in various biological processes, including enzyme function, cellular metabolism, and immune response. These elements help in enzymatic reactions and are often involved in the structural integrity of proteins or the transport of molecules within cells.

The other choices consist of macronutrients or elements that are required in larger amounts. Carbon, nitrogen, oxygen, and hydrogen are considered fundamental building blocks of organic molecules and are needed in greater quantities for such processes as energy production, building cellular structures, and maintaining metabolic functions. Thus, while they are crucial for life, they do not fit the definition of micronutrients in the same way that trace elements do.