$d-d$ transition occurs in . . . . . . .

Fill in the blanks:
$(a)$ The shielding effect of $d$-electrons is ......... effective than $p$-electrons.
$(b)$ $A$ decrease in exchange energy leads to a ......... in stability.
$(c)$ The maximum oxidation state of $Mn$ is ..........
$(d)$ The stability of $Mo(VI)$ and $W(VI)$ is found to be .......... than that of $Cr(VI)$.

Total number of $d$ electrons present in an element with atomic number $78$ is:

The magnetic moments for $Ti^{2+}$,$V^{3+}$,and $Ni^{2+}$ are respectively:

Which of the following metal ions will have the maximum number of unpaired electrons?

How many of the following lanthanide elements exhibit $+4$ oxidation state?
$Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy$