Which element has the atomic number 1?

The element with atomic number 1 is hydrogen. This is because the atomic number of an element is defined as the number of protons in the nucleus of an atom of that element. Hydrogen has a single proton in its nucleus, which gives it the atomic number 1. It is also the simplest and lightest of all the elements, consisting of one electron and one proton, making it fundamental in chemical reactions and the formation of more complex elements through processes such as nuclear fusion in stars.

Oxygen, helium, and lithium all have higher atomic numbers: oxygen has an atomic number of 8, helium is 2, and lithium is 3. Therefore, these elements are more complex than hydrogen and do not share its elemental properties or position in the periodic table. Hydrogens simple structure allows it to serve as a vital building block in various compounds, being a key component in water and organic molecules.