Element. All helium atoms have 2 protons. What is the atomic number of helium?

The only atom that contains one proton is the hydrogen atom, also called protium. It is neutrally charged with a single proton at its nucleus, and a single electron orbiting. It is possible that you are asking about the isotope of hydrogen called tritium. Tritium is a radioactive isotope of hydrogen that contains a single proton and two neutrons.