An unknown sample scatters light. When it is passed through a filter paper, it leaves some residue on the filter paper. The sample is most likely a
suspension
The given sample is a suspension. Suspensions scatter light when a beam of light is passed through it. The particles of suspension are relatively large and insoluble and can be separated using a filter paper. For example, if a suspension of sand and water is made to pass through a filter paper, the water passes through the filter paper while the sand is left behind on the paper.