There is some liquid in a closed bottle. The amount of liquid remains constant as time passes. The vapor in the remaining part.
1. Since the amount of liquid remains constant that means no vapors or moisture is being added to air or vapors above it.
2. Saturated air means air having maximum humidity or moisture. If we keep on adding moisture to saturated air the extra moisture will condense. And saturated air will become unsaturated air at temperature.
3. Since no moisture is being added, remaining vapors must be saturated.