The correct options are
B heat is released
C occupancy of π∗2p of O2 is increased
D bond length of O2 is increased
When O2 is adsorbed on a metallic surface, electron transfer occurs from the metal to O2.
The MO configuration of O2 is KK(σ2s)2(σ∗2s)2(σ2px)2(π2py)2(π2pz)2(π∗2py)1(π∗2pz)1
The MO configuration of O−2 is KK(σ2s)2(σ∗2s)2(σ2px)2(π2py)2(π2pz)2(π∗2py)2(π∗2pz)1
(A) Thus, oxygen is chemisorbed. Hence, the statement (A) is false.
(B) Chemisorption is an exothermic process. Heat is released. Hence, the statement (B) is true.
(C) The occupancy of π∗2p of O2 is increased. The added electron enters π∗2py MO. Hence, the statement (C) is true.
(D) The bond order is decreased (as the electron enters anti bonding MO) and the bond length of O2 is increased. Hence, the statement (D) is true.