What is a theoretical plate?

The fragrance of flowers is due to the presence of some steam volatile organic compounds called essential oils. These are generally insoluble in water at room temperature but are miscible with water vapour in the vapour phase. $A$ suitable method for the extraction of these oils from the flowers is:

The most suitable method of separation of a $1:1$ mixture of $ortho$- and $para$-nitrophenols is:

Suggest a method for the purification of camphor contaminated with salt.

The method used for the separation of the mixture of products ($B$ and $C$) obtained in the following reaction is:

Which one of the following techniques is not used to spot components of a mixture separated on a thin layer chromatographic plate?