Hydrogen and oxygen are examples of which of the following categories?

Hydrogen and oxygen are classified as elements because they are fundamental substances that cannot be broken down into simpler substances by chemical means. Each element is represented by a unique symbol on the periodic table, with hydrogen symbolized as 'H' and oxygen as 'O'.

Elements are distinguished by the number of protons in their atomic nuclei, which defines their chemical properties. Hydrogen is the simplest and lightest element with one proton, while oxygen has eight protons. Both are vital for various chemical processes, including combustion and respiration, and serve as building blocks for more complex compounds and molecules, but they themselves remain pure elements.

In contrast, isotopes refer to different versions of the same element that have the same number of protons but different numbers of neutrons. Molecules are formed when two or more atoms bond together, which can include atoms of the same element, like O2, or different elements. Compounds consist of molecules that contain at least two different elements chemically bonded together, such as H2O (water), which includes hydrogen and oxygen.