The correct answer is option 3: sublimation.

Sublimation is a process where a solid substance changes directly into a gas without going through the liquid phase. In the case of the mixture of sodium chloride and naphthalene, naphthalene can undergo sublimation while sodium chloride cannot.

Option 1, extraction with hot water, would not work in this case because both sodium chloride and naphthalene are insoluble in water. They would not dissolve and separate from each other.

Option 2, extraction with cold water, also would not work because both substances are insoluble in water regardless of its temperature.

Option 4, steam distillation, is a method used to separate substances with different boiling points, and is not suitable for separating sodium chloride and naphthalene.

Therefore, the only viable option for separating the mixture of sodium chloride and naphthalene is sublimation, where naphthalene can be heated to convert directly into a gas and leave behind the sodium chloride solid.