The d-block elements form alloys, as the d-block elements have similar atomic sizes due to which atoms of one metal can easily take up position in the crystal lattice of the other.
The atomic sizes of the d block elements are related or comparable to each other. Due to this one metal can easily replace the other and form another solid, which is called an alloy. An alloy is the homogeneous mixture of two or more metals or metals with non-metals. Hence d block elements form alloys.