Answer:
Heating
Step-by-step explanation:
Matter comprises of particles called atoms or molecules. Particles are held together by a strong force of attraction between them. The force of attraction is strongest in solids and weakest in liquids.
When matter is heated, the particles absorb the energy and start colliding with each other. The particles strike each other with force, causing the force of attraction between them to reduce.
As the force of attraction reduces, the particles move further apart from each other causing the space between them to increase.