The melting and boiling points of Zn, Cd and Hg are low.Why ?

Account for the following: There is large difference between the melting and boiling points of oxygen and sulphur.

Melting and boiling points of ionic compounds are high.

Why the melting and boiling points of alkynes are higher than alkenes and alkanes?

In general, the melting and boiling point of transition metals

Why compounds of Zn, Cd, Hg are generally white ?

Transition metals have high melting and boiling points. Why ?