Indicate the complex entity which shows optical isomerism.

Among $VO_2^{+}$,$MnO_4^{-}$ and $Cr_2O_7^{2-}$,the spin-only magnetic moment value of the species with least oxidising ability is $BM$ (Nearest integer). (Given atomic number $V=23$,$Mn=25$,$Cr=24$)

Which of the following compounds is diamagnetic?

Among the following complexes,the one that can exist as facial $(fac)$ and meridional $(mer)$ isomers is

Given below are two statements:
Statement $I$: $A$ homoleptic octahedral complex,formed using monodentate ligands,will not show stereoisomerism.
Statement $II$: $cis-$ and $trans-$ platin are heteroleptic complexes of $Pd$.
In the light of the above statements,choose the correct answer from the options given below.

Consider the following complex ions,$P$,$Q$ and $R$.
$P = [FeF_6]^{3-}$,$Q = [V(H_2O)_6]^{2+}$ and $R = [Fe(H_2O)_6]^{2+}$.
The correct order of the complex ions,according to their spin-only magnetic moment values (in $B.M.$) is