What element has the atomic number 1?

Hydrogen is the element with the atomic number 1, which means it is the simplest and lightest element on the periodic table. The atomic number of an element is determined by the number of protons in its nucleus, and since hydrogen has one proton, it holds the position of being the first element. This fundamental characteristic plays an important role in various scientific fields such as chemistry, physics, and even biology. In contrast, helium, oxygen, and lithium have higher atomic numbers, signifying that they contain more protons in their nuclei—helium has two, oxygen has eight, and lithium has three. Thus, hydrogen's unique atomic number highlights its significance as the most basic building block of matter in the universe.