Which of the following elements can form complex ions?

In which of the following ions,$d-d$ transition is not possible?

If an atom has electronic configuration $1s^2 2s^2 2p^6 3s^2 3p^6 3d^3 4s^2$,it will be placed in :-

Which of the following has a colored aqueous solution?

Calculate the number of unpaired electrons in the following gaseous ions: $Mn^{3+}, Cr^{3+}, V^{3+}$ and $Ti^{3+}$. Which one of these is the most stable in aqueous solution?

Which of the elements possess only one electron in the $5d$-orbital?