Give the answer of the following questions in short:
$(i)$ When is simple distillation used?
$(ii)$ When is fractional distillation used?
$(iii)$ Which liquid is obtained first in fractional distillation?
$(iv)$ Which liquid is cooled first in fractional distillation?
$(v)$ What happens in the fractional column?

(N/A) $(i)$ $(a)$ For the purification of volatile liquids. $(b)$ For the separation of liquids in which the difference in boiling point is more than $30^{\circ} C$.
$(ii)$ $(a)$ For the separation of liquids in which the difference in boiling point is small. $(b)$ In the petroleum industry to separate different components.
$(iii)$ The liquid which is more volatile and has a lower boiling point is obtained first.
$(iv)$ In fractional distillation,the condensation of the liquid with a higher boiling point takes place first,followed by the condensation of the liquid with a lower boiling point.
$(v)$ In the fractional distillation column,there is a heat exchange between the vapour moving upward and the liquid moving downward. The condensed liquid absorbs heat from the vapour and converts back into vapour. As a result,the concentration of the liquid with the lower boiling point increases in the vapour phase.