The 3d element with least melting point is

Cr, Mo, W of 6th group have the highest melting points in their respective transition series;

Due to the presence of more number of unpaired (n-1)d electrons and ns electrons the metallic bonding in chromium is strong;

Metallic bond strength $\propto$ Melting point ;

Due to s²d¹⁰ configuration the metallic bonds in Zn, Cd and Hg are very weak ;

Zinc family belongs to d-block but these are not transition elements ;

In copper family, M.P of Cu>Au>Ag ;