Which one of the following complexes shows optical isomerism? $(en = \text{ethylenediamine})$

Which one of the following is expected to exhibit optical isomerism $(en = \text{ethylenediamine})$?

Consider the complexes:
$I$. $[Pd(NH_3)_2 ClBr]$
$II$. $[Pd(NH_3)_2 Cl_2]$
$III$. $[Pd(en) Cl_2]$
$IV$. $[Pd(en) ClBr]$
$V$. $[Pd(en)_2 Cl_2]$
(en = ethylenediamine)
The total number of geometrical isomers of $(I)$ is the same as the total number of geometrical isomers of:

The magnetic moment of ${K_3}[Fe(CN)_6]$ is found to be $1.7 \ B.M.$ How many unpaired electron$(s)$ is/are present per molecule?

In an octahedral complex $[Mabcdef]$,the total number of theoretical isomers is:

Which of the following compounds is colored but does not contain any unpaired electrons?