Q.Why do transition elements form alloys ?

Transition metals readily form alloys because their atoms are similar in size, adopt similar metallic crystal structures, and have comparable chemical character, so they can substitute for one another in a shared metallic lattice.

An alloy is essentially a homogeneous solid solution of one metal in another (or in several others). Transition elements are especially prone to forming such alloys for a few closely related structural reasons:

1. Similar atomic radii: Across a transition series, the atomic radii of successive elements change only gradually (unlike the sharp changes seen across a typical main-group period), so neighbouring transition metals are close enough in size for one to be substituted for another in a crystal lattice without much lattice strain or distortion.
2. Similar crystal structures: Most transition metals crystallise in one of the same few close-packed metallic lattice types (body-centred cubic, face-centred cubic, or hexagonal close-packed), making it geometrically easy for atoms of a second transition metal to occupy lattice sites of the first. …