Transition elements exhibit variable oxidation states because they lose electrons from which of the following orbitals?

Which compound has a coloured aqueous solution?

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 $Cr(VI)$.

Identify the element for which the electronic configuration in the $+3$ oxidation state is $[Ar] 3d^5$:

The chloride of which of the following elements will be coloured?

Transition elements are: