Final answer:
The mixture of black iron filings and yellow sulfur powder is a heterogeneous mixture because its composition is not uniform and the individual substances are distinguishable.
Step-by-step explanation:
A mixture of black iron filings and yellow sulfur powder is a heterogeneous mixture. This type of mixture is characterized by its non-uniform composition, where the individual substances (iron filings and sulfur powder) maintain their own properties and can be observed as distinct parts. Unlike homogeneous mixtures, where components are uniformly mixed, a heterogeneous mixture doesn't have a consistent composition throughout.
Homogeneous mixtures, also known as solutions, appear as a single phase in which one cannot distinguish individual substances. However, in the case of iron filings mixed with sulfur powder, one can see two separate substances, hence it is not a homogeneous mixture. It is also not a compound because iron and sulfur are not chemically bonded together, nor is it a metal alloy, which would require the substances to be metals fused into a single, uniform material.