Introduction:
When non-metals like B (boron) and C (carbon) are added to the interstitial sites of a transition metal, it affects the properties of the resulting metal. Specifically, the metal becomes less ductile, less malleable, and harder.

Explanation:

1. Less Ductility:
Ductility refers to the ability of a material to be drawn into wires without breaking. When non-metals like B and C are added to the interstitial sites of a transition metal, they disrupt the regular arrangement of metal atoms. This leads to the formation of strong bonds between the metal atoms and the non-metal atoms, making it difficult for the metal to undergo plastic deformation. As a result, the metal becomes less ductile.

2. Less Malleability:
Malleability refers to the ability of a material to be hammered or rolled into thin sheets without breaking. The addition of non-metals like B and C to the interstitial sites of a transition metal also affects its malleability. The presence of these non-metal atoms creates localized regions of high atomic density, which makes it difficult for the metal to deform plastically. Consequently, the metal becomes less malleable.

3. More Hardness:
Hardness is a measure of a material's resistance to indentation or scratching. The addition of non-metals like B and C to the interstitial sites of a transition metal increases the hardness of the resulting metal. The non-metal atoms occupy the interstitial sites, which leads to distortion of the regular metallic lattice structure. This distortion increases the resistance of the metal to deformation, resulting in a harder material.

Summary:
In summary, the addition of non-metals like B and C to the interstitial sites of a transition metal results in a metal that is less ductile, less malleable, and harder. The presence of these non-metal atoms disrupts the regular arrangement of metal atoms, leading to the formation of strong bonds and localized regions of high atomic density. These changes in the structure of the metal affect its mechanical properties, making it less ductile and less malleable while increasing its hardness.