Is C2(-) paramagnetic or diamagnetic?

patamagnetic because it has odd numbers of electrons
All of the electrons are spin-paired in diamagnetic elements so their subshells are completed, causing them to be unaffected by magnetic fields. Paramagnetic elements are strongly affected by magnetic fields because their subshells are not completely filled with electrons. So, to determine whether the elements are paramagnetic or diamagnetic, write out the electron configuration for each element.
It is paramagnetic because it has an unpaired electron.