Answer:
Step-by-step explanation:
To purify a substance whose boiling point is so high that on reaching boiling point , the substance may undergo chemical change , we manage boiling of substance at relatively lower temperature . This can be done at reduced pressure . Boiling point is dependent on the external pressure. If external pressure is reduced , boiling can be managed at a temperature far below actual boiling point . In this way we can manage the substance to boil at lower temperature thus we can save the substance to undergo chemical change.