An element has three naturally occurring isotopes. The isotope with a mass number of 24 has an actural atomic mass of 23.985 amu and has a relative abundance of 78.99%. The idotope with a mass number of 25 has an actual atomic mass of 24.986 amu and a relative abundance of 10.00%. The isotope with a mass number of 26 has an actual tomic mass of 25.983 amu and has a relative abundance of 11.01%