Question

why transition metals are hard but non-transition metal are soft? why transition metals have high melting and boiling point whereas non transition have low?

Answer 1

Transition metals have electrons which are far from nucleus. These electrons are freely available for bonding and hence forms strong metallic bonding. Due to this they are hard. Whereas non transition metals the electrons are tightly hold by the nucleus, and they are not available for the bonding. So they are soft.
Due to strong metallic bonding they are tightly packed as a result the transition metal has high melting and boiling points. Due to weaker metallic bonding the non transition element has less boiling and melting points.