Final answer:
On a muggy day, when water molecules in the air contact our bodies, they are likely to condense due to high humidity in the air. The evaporation rate of sweat from the skin's surface is reduced, making sweat less likely to evaporate and more likely to condense, making the skin feel sticky.
Step-by-step explanation:
On a muggy day, water molecules in the air that strike our bodies are likely to condense. This is because on humid days, the air is already saturated with moisture, limiting the amount of additional water vapor that can be held in the air. Thus, when these water molecules come into contact with a cooler surface, such as human skin, they lose some of their kinetic energy and transition from a gaseous state (vapor) back to a liquid state in a process known as condensation. The concentration of water in the atmosphere on muggy days is higher, which reduces the evaporation rate from the skin's surface. Instead, you might feel the stickiness on your skin as sweat is less likely to evaporate and more likely to remain or condense on the skin.
Furthermore, on hot, dry days, the evaporation of sweat from the skin can cool the body because water molecules absorb body heat and evaporate from the surface of the skin, leaving the remaining perspiration cooler. However, this cooling effect is diminished on humid, muggy days because the high moisture content in the air impedes evaporation.