Correct any inaccuracies in the following statements and, after correction:

(a) Elements in the middle of Group 16 are easier to oxidize to the group oxidation number than are the lightest and heaviest members.

(b) In its ground state, O₂ is a triplet and it undergoes Diels–Alder electrophilic attack on dienes.

(c) The diffusion of ozone from the stratosphere into the troposphere poses a major environmental problem.