The electronic configuration of $Cr^{3+}$ is

Which of the following may be colourless?

Transition metals show paramagnetism.

Among $Sc$,$Mn$,$Co$ and $Cu$,identify the element with the highest enthalpy of atomisation. The spin-only magnetic moment value of that element in its $+2$ oxidation state is $......... \text{BM}$ (in nearest integer).

Gadolinium belongs to the $4f$ series. Its atomic number is $64$. Which of the following is the correct electronic configuration of gadolinium?

Although $Zr$ belongs to the $4d$ and $Hf$ belongs to the $5d$ transition series, it is quite difficult to separate them. Why?