How is the difference in the physical properties of the powdered mixture components being used to separate them in this lab

This question is incomplete but the missing part is in the picture attached.

Explanation:

A mixture of silicon oxide, ammonium chloride and sodium chloride were to be separated. Three separating techniques were used in the experiment; sublimation, decantation and evaporation.

Sublimation is the process in which a substance changes from solid to gas without passing through the liquid phase. Ammonium chloride (NH₄Cl) is a substance that has the ability to sublime and thus was separated first through this property before adding water to the remaining constituents (silicon oxide and sodium chloride) of the mixture. After the addition of water to the mixture, sodium chloride dissolves in this water while silicon oxide does not dissolve in water. The mixture is then left to stand for some minutes so the undissolved sand can settle at the bottom of the mixture and the dissolved salt water can be decanted out so as to have the silicon oxide left in the jar.

The salt solution decanted will have to be evaporated to dryness (to remove the added water) so as to have the solid salt back.

the answer is na (sodium)