The correct option for separating the constituents of a mixture containing SiO2, NaCl, and NH4Cl is option 1: Sublimation - dissolution - filtration - crystallisation.

Let`s dissect each step briefly for better understanding:

1. Sublimation: This step involves subliming the NH4Cl, which is a volatile component of the mixture. Sublimation is the process in which a solid directly converts into a gas without passing through the liquid state. By heating the mixture, NH4Cl sublimes, leaving behind SiO2 and NaCl.

2. Dissolution: After sublimation, the remaining mixture now consists of SiO2 and NaCl. To further separate them, the mixture is dissolved in a suitable solvent. Both SiO2 and NaCl are soluble in water, thus forming a homogeneous solution.

3. Filtration: The solution obtained from the previous step is then subjected to filtration. Filtration is a process where a physical barrier (a filter) is used to separate solid particles from the liquid solution. This step helps in separating the undissolved SiO2 from the NaCl solution.

4. Crystallisation: The filtrate (the liquid obtained after filtration) is then subjected to the