Strong reducing and oxidizing agents among the following , respectively, are

${\mathrm{E}}_{{\mathrm{Ce}}^{4+}/{\mathrm{Ce}}^{3+}}=+1.74 \mathrm{V}$

Lanthanoids have $+3$ oxidation state as stable oxidation state. Hence, in their $+4$ oxidation state, they act as an oxidising agents and  $+2$ oxidation state, they act as reducing agents.