Change in composition of the coordination sphere yields which type of isomers?

$[Co(en)_3]^{3+}$ ion is expected to show

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

$CoSO_{4}Cl \cdot 5NH_{3}$ exists in two isomeric forms '$A$' and '$B$'. Isomer '$A$' reacts with $AgNO_{3}$ to give white precipitate,but does not react with $BaCl_{2}$. Isomer '$B$' gives white precipitate with $BaCl_{2}$ but does not react with $AgNO_{3}$. Answer the following questions.
$(i)$ Identify '$A$' and '$B$' and write their structural formulas.
$(ii)$ Name the type of isomerism involved.
$(iii)$ Give the $IUPAC$ name of '$A$' and '$B$.'

Which of the following complexes will show coordination isomerism?
$A. [Ag(NH_3)_2][Ag(CN)_2]$
$B. [Co(NH_3)_6][Cr(CN)_6]$
$C. [Co(NH_3)_6][Co(CN)_6]$
$D. [Fe(NH_3)_6][Co(CN)_6]$
$E. [Co(NH_3)_6][Fe(CN)_6]$
Choose the correct answer from the options given below:

The value of the 'spin only' magnetic moment for one of the following configurations is $2.84 \ BM$. The correct one is: