The transition metal with the highest melting point is:

Among the following options,identify the element which exhibits the greatest number of oxidation states.

Pairs of elements with the same number of electrons in their respective $4f$ orbital are [Atomic number: $Eu-63, Gd-64, Dy-66, Ho-67, Tm-69, Yb-70, Lu-71, Hf-72$]. Choose the correct answer from the options given below:

Which one of the following exhibits the largest number of oxidation states?

Which of the following sets of ions contains colored ions?
$(1) \ Cu^{2+}$ $(2) \ Ti^{4+}$ $(3) \ Co^{2+}$ $(4) \ Fe^{3+}$

Based on the given outer electronic configurations,which element will exhibit the highest oxidation state?