The magnetic moment of $Ni^{2+}$ in an aqueous solution is ......... $B.M.$

Which of the following compounds has a magnetic moment identical to $[Cr(H_{2}O)_{6}]^{3+}$?

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

Choose the complexes which are paramagnetic from the following:
$(i)$ $K_4[Fe(CN)_6]$
(ii) $K_3[Cr(CN)_6]$
(iii) $K_3[Fe(CN)_6]$
(iv) $K_2[Ni(CN)_4]$

Which of the following complexes exhibit geometrical isomerism?
$I$) $[Co(en)(NH_3)_2 Cl_2] Cl$
$II$) $[Co(NH_3)_4 Cl_2] Cl$
$III$) $[Co(en)_3] Cl_3$
$IV$) $[Co(en)_2 Cl_2] Br$

Identify the optically active compound from the following.