When snow melts does its volume decrease or increase?

The volume of the snow decreases. This had happened because the snow is made up or comprised of water (H2O) and oxygen (O). When the snow starts melting, the air inside the snow discharges into the atmosphere and the water turn out to be a puddle on the ground. 

in chemistry, adhesion and cohesion are attractive forces that exist between molecules. they hold the molecules together from each other. they are different in that adhesive force exists between molecules of different substance while cohesive force happens between molecules of same substance.

adhesion between water and glass causes water molecules at the edge of water and glass interface to climb up the wall in a narrow glass tube. this is called capillary action. cohesion is what gives glass its shape and causes water to form a droplet.