Which compound is an example of an interstitial compound?

An interstitial compound is formed when smaller atoms occupy the interstitial spaces or voids between the larger metal atoms in a crystalline structure. This type of compound typically consists of a metal and a non-metal, where the smaller non-metal atoms fit into the gaps of the metal lattice, resulting in altered properties compared to the pure metals involved.

In the case of Fe3C, also known as cementite, it is composed of iron (Fe) and carbon (C). The carbon atoms are much smaller than the iron atoms, allowing them to occupy the spaces between the iron atoms in its crystal structure. This enhances the hardness and strength of the iron, making Fe3C an important phase in steel and cast iron.

The other compounds listed do not exemplify interstitial compounds. For example, Al2O3, while a compound of aluminum and oxygen, does not feature the same type of interstitial arrangement. Similarly, CuZn, which indicates a solid solution or alloy, does not contain any interstitial inclusions. Lastly, AgCl is an ionic compound without the necessary metallic lattice for interstitial solid formation. Thus, Fe3C distinctly fits the definition of an interstitial compound.