Transition elements form complex compounds due to:

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:

Metal-metal bonding is more frequent in $4d$ or $5d$ series than in $3d$ series due to

The transition metal with the highest melting point is:

What is the numerical value of spin only magnetic moment of copper in $+2$ state?

Which of the following species is expected to show the highest magnetic moment? (At. Nos.: $Cr = 24$,$Mn = 25$,$Co = 27$,$Ni = 28$,$Cu = 29$)