What are the basic difference between the two geometrical isomers – cis/trans or fac/ mor?

Why is geometrical isomerism not possible in tetrahedral complexes having two different types of unidentate ligands coordinated with the central metal ion ?

Give two examples of positive mono-denate ligands. 

Which isomer of  [CoCl₂(en)₂]⁺ does not show optical isomerism?

Specify which out of the following complex structures exhibit geometrical isomerism:
(a) Linear,   (b) Square planar,  (c) Tetrahedral, (d) Octahedral.

Draw structures of geometrical isomers of [Fe(NH₃)₂(CN)₄]^–.

Write the chemical formula of:
(i) Sodium tetrahydridoborate(III).
(ii) Tetrahydroxo zincate(II) ion.

Write all isomers of [Co(C₂O₄)₃]^3–.

Give an example of hexadentate ligand.