Final answer:
Distillation is the best method to separate a mixture of ammonium chloride, sand, and zinc chloride by making use of the different boiling points and the ability of ammonium chloride to sublime.
Step-by-step explanation:
The best means to separate a mixture of ammonium chloride, sand, and zinc chloride would be distillation. This method leverages the differences in boiling points to separate substances. Ammonium chloride sublimes, meaning it can directly transition from a solid to a gas without becoming a liquid, at a lower temperature than zinc chloride's boiling point. By slowly heating the mixture, ammonium chloride can be separated first, followed by the evaporation of zinc chloride. The remaining component, sand, which is insoluble and has a high boiling point, is left behind.
During distillation, the vapor formed from the most volatile substance (ammonium chloride, then zinc chloride) is condensed back to a liquid in a condenser and collected separately. Filtration will not be effective since both chlorides can dissolve in water, and decantation cannot separate dissolved substances. Evaporation could also be used but would not separate the chlorides efficiently from each other; hence, distillation is the best choice.