Explain why a solid mothball disappears without leaving any liquid & why our skin feels cold when a little alcohol is rubbed on it?

Some substances change from solid to the vapour state
without passing through the intermediate liquid state. This process of materials
changing from solid to directly vapour state is called sublimation, and the material
that exhibit the property of sublimation are called sublime material. Some example such
material are iodine, arsenic, camphor, and dry ice. There are a few substances, such as
iodine, arsenic, camphor, and dry ice. Mothballs are deliberately made of sublime
substances so as liquids substances can soil the material to be protected against
mothballs.

Our skin feels cold when alcohol is rubbed on it
because of the latent heat of evaporation absorbed by the alcohol when it evaporates.
Alcohol has very low boiling point and evaporates very fast even at room temperature.
Because of this, during evaporation it absorbs heat from the skin faster than other
liquids like water, making the skin feel cooler.