Indicate the complex entity which shows optical isomerism.

Which of the following outer octahedral complexes have the same number of unpaired electrons?
$1$. $[MnCl_6]^{3-}$
$2$. $[FeF_6]^{3-}$
$3$. $[CoF_6]^{3-}$
$4$. $[Ni(NH_3)_6]^{2+}$

Which of the following complexes will exhibit optical isomerism?

What is the value of spin-only magnetic moment for $Cu^{2+}$ in $BM$?

The metal ions that have the calculated spin-only magnetic moment value of $4.9 \ B.M.$ are:
$A. Cr^{2+}$ $B. Fe^{2+}$ $C. Fe^{3+}$ $D. Co^{2+}$ $E. Mn^{3+}$
Choose the correct answer from the options given below:

The type of isomerism present in pentaammine nitro chromium$(III)$ chloride is