Which element has the atomic number 1?

Hydrogen is the element with the atomic number 1, which signifies that it has one proton in its nucleus. The atomic number is a fundamental property that defines the identity of an element, as it determines the number of protons, which in turn dictates the element's position on the periodic table and its chemical behavior. For hydrogen, being the simplest and most abundant element in the universe, it consists of only one proton and one electron, making it the lightest element.

The other elements listed have higher atomic numbers: oxygen has an atomic number of 8, helium is 2, and lithium is 3. This order reflects their respective numbers of protons, confirming that hydrogen, with its atomic number of 1, is unique in its simplicity and foundational role in chemistry and the universe.