Which one of the following can be purified by sublimation?

The species that exhibits the highest $R_f$ value in a thin layer chromatogram using a non-polar solvent on a silica gel plate is

Which of the following statements are correct?
$A$. Glycerol is purified by vacuum distillation because it decomposes at its normal boiling point.
$B$. Aniline is purified by steam distillation as it is immiscible in water.
$C$. Ethanol can be separated from an ethanol-water mixture by azeotropic distillation because it forms an azeotrope.
$D$. An organic compound is pure if the mixed $M.P.$ remains the same.
Choose the most appropriate answer from the options given below:

What is $R_f$?

What is a theoretical plate?

Ethylene has a high $b.p.$ and high vapour pressure at $100\,^{\circ}C$ and does not dissolve in water. Hence,ethylene is separated by this method: