well if all f block elements lies on group 3, then why all their valency is not 3.n why the all r so different in the periodic table.....

well all as u said do not show +3 oxidation.... but itz consider as d mostly exibited state....

here in this case d elemets opt d valancy by wch they get d most stable state..... therefore +2 & +4 states r exibited to get half filled and full filled orbitals. but still they r unstable in +2 & +4 state and thus they reverse bck to +3 state.

and when it comes to its odd behaviou...... itz all because of it f-orbital...... wch is very typical........!!!! due to various reasons lik poor sheliding effect etc,....!!!!