Aclear liquid in an open container is allowed to evaporate. after three days a solid residue is left. was the original liquid an element, compound, or mixture? how do you know?

The clear liquid was allowed to evaporate and after 3 days, only solids are left. Therefore this means that for the 3 days it was exposed to air, some liquid or water perhaps was leaving out of the solution. Therefore this means that the liquid was a mixture. It was a initially a mixture of the solid residue plus the evaporated liquid.

It cannot be an element or a compound since both uniformly evaporates.

Mixture