Magnesium 26 is greater in atomic size than magnesium 24.
Work Step by Step
Magnesium 24 has 12 protons and 12 neutrons while Magnesium 26 has 12 protons and 14 neutrons. Therefore Magnesium 26 is greater in size by 2 neutrons. Magnesium 27 would be greater again. Magnesium always has 12 protons, that is what makes is magnesium. The neutrons changing make it a magnesium radioisotope. The greater the neutron the greater size.