Answer
Charcoal, which has a lower density than water, will float, while sand will remain in the bottom. We could then separate the two and dry the sand again.
Work Step by Step
Sugar is soluble in water, whereas charcoal and sand are not. Therefore, we will assume that if we stir the mixture and wait, the sugar will be completely dissolved in the water and the sand and the charcoal have sunk to the bottom of whichever container we are using or floated (in the case of charcoal). If this is the case, we can decant the water-sugar mixture. The sand-charcoal mixture will remain wet, however, so we may dry it with a lamp. Once the charcoal-sand mixture is dry, we now must consider the size of the charcoal pieces to proceed. If the charcoal pieces are considerably large, we could simply separate them manually. If they are not too small (considerably larger than sand) we could filtrate the mixture to separate it. Otherwise, now that the sample contains (theoretically) no sugar, we can add water again. Charcoal, which has a lower density than water, will float, while sand will remain in the bottom. We could then separate the two and dry the sand again.
