Correct Answer: Option 4 – Temperature

How matter changes its state:
The state of matter (solid, liquid, gas) mainly depends on temperature and pressure. Among these, temperature is the most important factor.

Effect of temperature:
Heating:
When temperature increases, particles gain energy, move faster, and overcome attractive forces.
Solid → Liquid (melting)
Liquid → Gas (boiling/vaporization)

Cooling:
When temperature decreases, particles lose energy and move closer together.
Gas → Liquid (condensation)
Liquid → Solid (freezing)

Effect of pressure:
Increasing pressure can compress gases into liquids (like LPG formation).
Decreasing pressure can help liquids turn into gases more easily.

Why other options are incorrect:
Volume: changes as a result of state change, not the cause.
Density: also changes after state changes, not responsible for them.
Shape: changing shape does not change the state of matter.