Q.Transition metals, with a few exceptions, are extremely hard and less volatile. Explain.

Physical Properties of Transition Metals

Transition metals (the d-block elements) share a set of characteristic physical properties: they are hard, dense, high-melting and high-boiling, and have low volatility. Iron, chromium and tungsten are typical — tungsten melts at about $3410\ ^\circ\text{C}$, the highest of any metal.

The origin of these properties is strong metallic bonding. In a transition metal, both the $ns$ and the unpaired $(n-1)d$ electrons participate in bonding, giving a large number of bonding electrons per atom. This is reflected in a high enthalpy of atomisation — the energy needed to convert the solid into free gaseous atoms. The more unpaired d-electrons available for bonding, the stronger the bond and the higher the melting point.

Worked comparison / trend: Across a series, melting points rise to a maximum near the middle (where the maximum number of unpaired d-electrons is available) and then fall. …