Why are different colours observed in octahedral and tetrahedral complexes for the same metal and same ligands?

CoSO₄Cl. 5NH₃ exists in ywo isomeric forms 'A'  and 'B' . Isomer 'A' reacts with AgNO₃ to give white precipitate, but does not react with BaCl₂. Isomer 'B' gives white precipitate with BaCl₂ but does not react with AgNO₃. Answer the following questions.
(i) Identify 'A' and 'B' and write their structural formulae.
(ii) Name the type of isomerism involved.
(iii) Give the IUPAC name of 'A' and 'B'.

Arrange the following complex in the increasing order of conductivity of their solution :
\([Co(NH_3)_3Cl_3],\ [Co(NH_3)_4Cl_2]\ Cl,\ [Co(NH_3)_6]\ Cl_3,\ [Cr(NH_3)_5Cl]\ Cl_2.\)

\(\)

A complex of the type [M(AA)₂X₂]ⁿ⁺ is known to be optically active.  What does this indicate about the structure of the complex ?  Give one example of such complex.