Suppose a lab group reports a percent yield of 90% of salt, What is a possible explanation for the "missing" product?
Most synthetic chemists would be quite prepared to cop a 90% yield.
So how could the losses occur? Losses in handling; i.e. the students did not scrape out their filter as well as they might. The solvent used to wash the crystals, dissolved some part of them, so that this mass ended up in the filtrate and was not collected. The students were cack-handed when they measured the mass, and some of the mass was lost from the sample. Almost any scenario is conceivable.