Final answer:
The bond order of the carbide dianion C2^2- is 3, indicating a triple bond and stability.
Step-by-step explanation:
The bond order of the carbide dianion C22- can be determined by examining its valence electron configuration and molecular orbital diagram. The valence electron configuration of C2 is (2s)2(2p)2(2py) (2pz) with a total of 6 bonding electrons and 2 antibonding electrons. Adding two more electrons to form C22- gives a valence electron configuration of (2s)2(2p)2(2py) (2pz)2(2px)1 with a total of 8 bonding electrons and 2 antibonding electrons. Therefore, the bond order is calculated as (8 - 2) / 2 = 3, indicating a triple bond and a stable ion.