+3 oxidation state of lanthanides is more stable why?

+3 oxidation state of lanthanides is more stable why?

The most common and stable oxidation state of Lanthanides is +3.It is attained by removing outermost 2 electrons of 6s electrons and 1 electron from 4f electrons. It is due to high energy difference in 4f and 6s, it is difficult to remove more electrons from 4f sub-shell.