Answer
See explanation below.
Work Step by Step
a.Electronic configuration of Ce2+ is [Xe]5d1 4f1
Electronic configuration of Ce3+ is [Xe]4f1
Electronic configuration of Ce4+ is [Xe]
b.Electronic configuration of Yb2+ is [Xe]4f14
Electronic configuration of Yb3+ is [Xe]4f13
Electronic configuration of Yb4+ is [Xe]4f12
c.Yb2+ has half filled subshell and Ce4+ has noble gas configuration.