Answer is: C. The substance is a heterogeneous mixture.
This substance is not element or compound, because different components could be observed in the substance.
Pure substance is made of only one type of atom (element) or only one type of molecule (compound), mixtures and solutions are made from two or more types of pure substances.
For example, aluminium is an element and ammonia is compound.
This substance is not a homogeneous mixture, because different samples of the substance appeared to have different proportions of the components.
Heterogeneous mixture is not uniform in composition.
For example, sand and small pebbles, proportions of its components (mixture particles of different colors and size) vary throughout the sample.
