Beryllium has 4 electrons, arranged 1s2 2s2. Written on the previous noble gas that is [He] 2s2, and the shells hold 2, 2 electrons from the innermost outwards.
Every subshell is either full or empty, so the ground-state atom has no unpaired electron and is diamagnetic.
The periodic table, read every way a chemistry course asks for. This tool needs JavaScript; these are the pages it offers: