What is mass?

Mass/melt/dissolve

Mass of an object is the amount of matter in that object. It does not depend on gravity but is proportional to the object's weight.
When an object melts when heated, it turns itself from a solid to become a liquid. For example, ice melts into water.
When an object is dissolved in a solvent, its molecules spread evenly in the solvent to form a solution. For example, salt is dissolved in water to form brine (salt solution).

Mass: quantity of matter without a regular shape(團，塊，堆)

Melt: make something become liquid through heating(令一樣物件融化)

Dissolve: make a solid become liquid(使固體溶解)