Melting points for transition metals of 3d, 4d and 5d series in general follows the order as …………
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 5d > 4d > 3d
Transition metals have high melting points because of strong metallic bonding. Besides the ns electrons, the unpaired (n−1)d electrons also take part in bonding between the atoms, so the bonds are very strong. Within a series the melting point rises to a maximum near the middle (d5), where the number of unpaired d electrons is greatest.
Going down a group, the 4d and 5d orbitals are larger and overlap better with those of neighbouring atoms, so the metal–metal bonding becomes stronger. The metals of the second and third series therefore have higher melting points than those of the first series, and the 5d metals are the highest. For group 6, for example:
Cr (3d) 2130 K < Mo (4d) 2890 K < W (5d) 3683 K
So in general the melting points follow the order 5d > 4d > 3d.
NCERT (2026-27 edition):
Physical Properties – …
