What is a hydroxide ion composed of?

A hydroxide ion is composed of one oxygen atom and one hydrogen atom, which is why option B is the correct choice. The hydroxide ion is represented chemically as OH⁻, indicating that it has one oxygen atom covalently bonded to one hydrogen atom, and carries a negative charge due to an extra electron. This ion plays a crucial role in various chemical processes, including its significance in acid-base chemistry, where it acts as a base by accepting protons.

The other options do not accurately describe the composition of the hydroxide ion. Two hydrogen atoms, two hydrogen atoms with one oxygen, or two oxygen atoms with one hydrogen do not correspond to the chemical structure of hydroxide.