What will be the atomic number of helium ion? 1 or 2?

A helium ion would have an of 2.

The atomic number does not change when an atom becomes an ion. This is because the atomic number is the number of protons in the nucleus, and an ion is formed when an atom gains or loses electrons, which are located in the electron cloud surrounding the nucleus. So a helium ion would have an atomic number of 2, which is the atomic number for helium.