What is melting? when an ice cube turns from a solid to a liquid, the particles

Melting is the breaking of bonds between particles (atoms) due to the increase in temperature (energy).

Explanation:

When elements are in solid form, it means that the conditions they are in do not allow particles to move much, which creates stable bonds (stable bonds as in, difficult to break) between atoms.  

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When the temperature increases, this atoms gain more and more energy (which makes them move) until bonds break and the transition from solid to liquid begins.

Hope it helped,

BioTeacher101