When $O_{2}$ is adsorbed on a metallic surface,electron transfer occurs from the metal to $O_{2}$. The $TRUE$ statement$(s)$ regarding this adsorption is(are)
$(A)$ $O_{2}$ is physisorbed
$(B)$ heat is released
$(C)$ occupancy of $\pi_{2p}^{*}$ of $O_{2}$ is increased
$(D)$ bond length of $O_{2}$ is increased

• A
  $(B, C, D)$
• B
  $(A, B, C)$
• C
  $(A, B, D)$
• D
  $(A, C, D)$