Suggest a method for the separation of a mixture of $o$-nitroaniline and $p$-nitroaniline.

Which purification method is used to separate a volatile liquid from non-volatile impurities?

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?

Given below are two statements:
Statement-$I$: Retardation factor $(R_f)$ can be measured in $meter/centimeter$.
Statement-$II$: $R_f$ value of a compound remains constant in all solvents.
Choose the most appropriate answer from the options given below:

Which of the following compounds is used as an adsorbent in column chromatography?

Describe the simple distillation method for the purification of liquid compounds.