The atomic mass of chromium is 51.9961 atomic mass units. The atomic mass is the average mass of an atom of a particular element. It is roughly the number of protons plus neutrons in an atom of the element.
The number is not exact because it constitutes an average of the number of protons and neutrons among the various isotopes of the element. Chromium has an atomic number of 24. It has 24 protons, 24 electrons and 28 neutrons, but the number of neutrons vary among the isotopes. Chromium is a transition metal discovered in 1797 and used in stainless steel.