What is the spin-only magnetic moment value $(BM)$ of a divalent metal ion with atomic number $25$ in its aqueous solution?

$[Co(NH_3)_5Br]SO_4$ and $[Co(NH_3)_5SO_4]Br$ are examples of which type of isomerism?

Which of the following will have three stereoisomeric forms?
$(i)$ $[Cr(NO_3)_3(NH_3)_3]$
$(ii)$ $K_3[Co(C_2O_4)_3]$
$(iii)$ $K_3[CoCl_2(C_2O_4)_2]$
$(iv)$ $[CoBrCl(en)_2]$

The 'spin only' magnetic moment value of $MO_4^{2-}$ is . . . . . $BM$. (Where $M$ is a metal having least metallic radii among $Sc, Ti, V, Cr, Mn$ and $Zn$).
(Given atomic number: $Sc=21, Ti=22, V=23, Cr=24, Mn=25$ and $Zn=30$)

The compounds $[Cr(H_2O)_6]Cl_3$,$[Cr(H_2O)_5Cl]Cl_2 \cdot H_2O$ and $[Cr(H_2O)_4Cl_2]Cl \cdot 2H_2O$ exhibit:

The number of isomers possible for the octahedral complex $[CoCl_{2}(en)(NH_{3})_{2}]^{+}$ is,