Students are given a solid sample and asked to determine whether the sample is an element, compound, or mixture. One student observes that the sample is: made up of particles of different colors, sizes, and shapes
some particles are softer than others
some shine while others appear dull
What can the students conclude about their sample?

It is an element.

It is a compound.

It is a homogeneous mixture.

It is a heterogeneous mixture.