Answer:
1. Solid to liquid - melting (ice to water)
2. Liquid to gas - vaporization (water to water vapor)
3. Liquid to solid- crystallization (freezing - water to ice)
4. Gas to liquid - condensation (making liquid nitrogen)
5. Gas to plasma - ionization
More rarely observed is :
6. Solid to gas (sublimation - dry ice to carbon dioxide)