Solution

When $$O_2$$ is adsorbed on a metallic surface, electron transfer occurs from the metal to $$O_2$$.
The MO configuration of $$O_2$$ is $$KK(\sigma 2s)^2(\sigma ^* 2s)^2(\sigma 2p_x)^2(\pi 2p_y)^2(\pi 2p_z)^2(\pi ^* 2p_y)^1(\pi ^* 2p_z)^1$$
The MO configuration of $$O_2^-$$ is $$KK(\sigma 2s)^2(\sigma ^* 2s)^2(\sigma 2p_x)^2(\pi 2p_y)^2(\pi 2p_z)^2(\pi ^* 2p_y)^2(\pi ^* 2p_z)^1$$
(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 $$ \pi ^*_{2p}$$ of $$O_2$$ is increased. The added electron enters $$\pi ^* _{2p_y}$$ 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 $$O_2$$ is increased. Hence, the statement (D) is true.