Which of the following compounds will exhibit coordination isomerism?

Number of complexes from the following with an even number of unpaired $d$ electrons is . . . . . . . . . .
$[V(H_2O)_6]^{3+}, \quad [Cr(H_2O)_6]^{2+}, \quad [Fe(H_2O)_6]^{3+}, \quad [Ni(H_2O)_6]^{3+}, \quad [Cu(H_2O)_6]^{2+}$
[Given atomic numbers: $V=23, Cr=24, Fe=26, Ni=28, Cu=29$]

The pair in which both the species have the same magnetic moment (spin only) is

In which case is a racemic mixture obtained upon mixing its mirror images ($d$ and $l$ forms) in a $1:1$ molar ratio?

Which one of the following complexes will most likely absorb visible light? (At. nos. $Sc = 21$,$Ti = 22$,$V = 23$,$Zn = 30$)

An octahedral complex with molecular composition $M \cdot 5NH_3 \cdot Cl \cdot SO_4$ has two isomers,$A$ and $B$. The solution of $A$ gives a white precipitate with $AgNO_3$ solution and the solution of $B$ gives a white precipitate with $BaCl_2$ solution. The type of isomerism exhibited by the complex is