Number of electrons present in $4\mathrm{f}$ orbital of ${\mathrm{Ho}}^{3+}$ ion is ________ (Given Atomic No. of $\mathrm{Ho}=67$)

The correct order of following $3\mathrm{d}$ metal oxides, according to their oxidation numbers is :

(a) ${\mathrm{CrO}}_3$

(b) ${\mathrm{Fe}}_2{\mathrm{O}}_3$

(c) ${\mathrm{MnO}}_2$

(d) ${\mathrm{V}}_2{\mathrm{O}}_5$

(e) ${\mathrm{Cu}}_2\mathrm{O}$

Statement I : ${\mathrm{CeO}}_2$ can be used for oxidation of aldehydes and ketones.

Statement II : Aqueous solution of ${\mathrm{EuSO}}_4$ is a strong reducing agent. In the light of the above statements, choose the correct answer from the options given below: