Camphor in nitrogen gas is a type of solution:

The correct option is Solid– Gas.

To understand why this is the correct classification, let us break down the components of a solution:
1. Solute: The substance that is dissolved in another substance (usually present in a smaller amount). In this case, camphor is the solute. Camphor exists as a solid at room temperature.
2. Solvent: The medium in which the solute is dissolved (usually present in a larger amount). In this case, nitrogen gas is the solvent, which is in the gaseous state.

When camphor is mixed with nitrogen gas, camphor (a solid) undergoes sublimation and disperses into the nitrogen gas (a gas). Since the solute is a solid and the solvent is a gas, this type of mixture is classified as a Solid– Gas solution.