Which of the following complex ions exhibits geometrical isomerism?

$(a) \ CoCl_{3} \cdot 4 NH_{3}$
$(b) \ CoCl_{3} \cdot 5 NH_{3}$
$(c) \ CoCl_{3} \cdot 6 NH_{3}$
$(d) \ CoCl(NO_{3})_{2} \cdot 5 NH_{3}$
Number of complex(es) which will exist in $cis-trans$ isomerism is/are ....

$A$ chromium complex with a formula $CrCl_3 \cdot 6H_2O$ has a spin-only magnetic moment value of $3.87 \ BM$ and its solution conductivity corresponds to a $1:2$ electrolyte. $2.75 \ g$ of the complex was dissolved and passed through a cation exchanger. The solution obtained after the process was reacted with excess $AgNO_3$. The amount of $AgCl$ formed in the above process is . . . . . . $g$. (Nearest integer) [Given: Molar mass in $g \ mol^{-1}$: $Cr = 52, Cl = 35.5, Ag = 108, O = 16, H = 1$]

Which of the following will show optical isomerism?
$I$. $\text{Cis}-[Co(NH_3)_2(en)_2]^{3+}$
$II$. $\text{Trans}-[IrCl_2(C_2O_4)_2]^{3-}$
$III$. $[Rh(en)_3]^{3+}$
$IV$. $\text{Cis}-[Ir(H_2O)_3Cl_3]$

The magnetic moment of a transition element is $\sqrt{15} \, B.M.$ Determine the number of unpaired electrons present in it.

$[Co(NH_3)_5SO_4]Br$ and $[Co(NH_3)_5Br]SO_4$ are a pair of isomers.