The correct answer to the question is option 1: sublimation.

Sublimation is a process in which a solid substance directly transforms into a vapor without passing through the liquid phase. In the case of a mixture of sodium chloride (salt) and ammonium chloride, the difference in their sublimation points allows for the separation.

Ammonium chloride has a lower sublimation point compared to sodium chloride. When the mixture is heated, the ammonium chloride will sublime, converting directly from a solid to a vapor. The vapor can then be collected and cooled back into a solid form, separate from the remaining sodium chloride.

Filtration (option 2) is not suitable in this case because both sodium chloride and ammonium chloride are soluble in water, and filtration is typically used to separate a solid from a liquid.

Chromatography (option 3) is used for separating mixtures that have different components with different affinities for a stationary phase and a mobile phase. It is not ideal for separating sodium chloride and ammonium chloride.

Distillation (option 4) is a technique used to separate mixtures based on differences in boiling points. However, since both sodium chloride and ammonium chloride are stable compounds at higher temperatures and do not have significant