What is the atomic number of Hydrogen?

Atomic number, Z = 1.

The atomic number of an element is the number of protons one of its atom contains. One neutral atom of Hydrogen contains one electron, one proton and 0,1,2 or 3 neutrons depending on which it is.

Fact: Even though Hydrogen is so small, it constitutes 75% of the elemental mass of the whole universe!