Which species is diamagnetic and have shortest bond length?

Among the following molecules/ions, C_(2)^(2-), N_(2)^(2-), O_(2)^(2-), O_(2) Which one is diamagnetic and has the shortest bond length?

Among the following molecules/ions C_(2)^(2-),N_(2)^(2-),O_(2)^(2-),O_(2) Which of one diamagnetic and has the shortest bond length?

Which of the species is diamagnetic ?

Which of the following species has the shortest bond length? N_2^(+) , N_2 , N_2^(-) , N_2^(2-)