Fill in the blanks with the correct word/s from the bracket.
Ice on absorption of heat converts to $$X$$ a process called ___________ [vaporization / melting]. $$X$$ changes to water vapour on ___________ [heating / cooling]. Water vapour changes back to $$X$$ on ___________ [freezing / condensation]. The constant temperature at which ice changes into $$X$$ is called its ___________ [fusion point / melting point / boiling point).