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

Which of the following compounds does not exhibit optical isomerism? $(en = \text{ethylenediamine})$

Identify the metal ions among $Co^{2+}, Ni^{2+}, Fe^{2+}, V^{3+}$ and $Ti^{2+}$ having a spin-only magnetic moment value more than $3.0 \ BM$. The sum of unpaired electrons present in the high spin octahedral complexes formed by those metal ions is . . . . . . .

$A$ compound absorbs light in the wavelength region $490-500 \,nm$. Its complementary colour is

$A$ metal complex of coordination number six having three different types of ligands $a$,$b$ and $c$ of composition $Ma_2b_2c_2$ can exist in several geometrical isomeric forms; the total number of such isomers is

What type of isomerism is exhibited by $[Co(NH_3)_6][Cr(CN)_6]$ and $[Cr(NH_3)_6][Co(CN)_6]$?