Q.11. In cyclic trimer of $S{O}_3$(i.e. $S_3{O}_9$) the number of oxygen atoms bonded to each sulphur atom is:

SO₃ trimer is when it is condensed, pure SO₃ gas forms an ice-like trimer which is cyclic. This is also called γ-SO₃.

cyclic-SO₃ trimer

Hence,The number of oxygen atoms bonded to each sulphur atom is 4