Question

Why does air at 75% relative humidity and 30°C make your skin feel stickier than air at 75% relative humidity at 10°C?

Warm air rises while cold air falls.
The warmer air contains less water vapor per unit of volume.
The warmer air contains more water vapor per unit of volume.
Moist air has lower density than dry air does.

Answer 1

The warmer air contains less water vapor unit of volume 

Answer 2

The warm air contains more water vapour per unit volume.

Explanation: Relative humidity is the amount of moisture present in the air. In other word relative humidity is the moisture holding capacity of the air. If the temperature increases the spaces between the air molecules also increase. It can hold more moisture.

In cool air the moisture is less retained in air as it has already moisture in it. This is called dew point. This also cause condensation, rain etc. This is the very reason in winter skins are chapped or dry. But in summer due to dry air the humidity is more and we feel sweaty and sticky skin.

That's why in 75% relative humidity, having high temperature make our skin sticky than 10 degree centigrade.