Which element has the atomic number 1?

The element with the atomic number 1 is hydrogen. The atomic number of an element is defined by the number of protons in its nucleus. In the case of hydrogen, it has one proton, which gives it an atomic number of 1. This unique identification distinguishes hydrogen from other elements, such as helium, lithium, and oxygen, which have higher atomic numbers due to having more protons in their nuclei. Helium has an atomic number of 2, lithium has an atomic number of 3, and oxygen has an atomic number of 8. Therefore, hydrogen's designation as the first element in the periodic table signifies its fundamental role in the universe and is critical in various chemical reactions, notably in the formation of water and hydrocarbons.