Why do d-block elements form alloys?

Hint: Modern periodic table consists of 18 vertical columns known as groups arranged as left to right and seven horizontal rows known as periods arranged from top to bottom. In this periodic table elements are arranged according to their atomic number and this table divides the elements into s, p, d and f-block elements on the basis of their valence shell electrons.

Complete answer:
Group 1,2,13-17 are known as main group elements in which the last electron will enter in s or p subshell, group 3-12 are known by the name transition elements and also called d-group elements and group 18 is of inert gases or noble gases i.e. those elements which have fully filled outermost atomic shell and have high stability. Rather than this there are two rows below the table known as inner transition elements in which the last electron will enter into the f-subshell.
d-block elements also known as transition elements have a tendency to form alloys; this can be explained on the basis that the atomic size of the elements are related or comparable to each other. Due to this a metal can easily replace other metal and form another solid which is known as alloy of that metal. We know that alloy is a homogeneous mixture of two or more metals or non-metals.
Hence in this way we can explain that d-block elements form alloys.

Note:
An alloy may be a solid solution of metal elements in which all metallic crystals are of the same composition or a mixture of metallic phases. Alloys are defined by a metallic bonding character. The alloy constituents are usually measured by mass percentage for practical applications.