The given question is not complete, the complete question is:
There are many chemicals that can be used to visualize spots on a tlc plate that have been run and dried. The permanganate used in the video to make the yellow spots on the purplish background relies on the oxidizing power of basic permanganate (MnO4) solutions, which is a stronger oxidizing agent than chromic acid. You could also use chromic acid to visualize spots, and the yellow background would turn green wherever something is being oxidized. So, could you use easily use chromic acid to visualize spots when you are monitoring a reaction to make a ketone out of an alcohol? What would you likely observe if you tried? Also, if used a little alcohol in a solvent mixture to elute your tic plate, why is it important to completely dry the plate before you visualize your spots using an oxidizing agent such a permanganate or chromic acid?
Answer:
Generally, the reactions in which the conversion of alcohol is done to a ketone cannot be monitored with the help of chromic acid. The substrate, that is, alcohol will transform into the corresponding ketone with the application of chromic acid. Thus, both the product’s and the reactant's spots will fall in a similar horizontal line. So, it would become tough to differentiate the spots, due to which chromic acid is not an appropriate chemical to use in the process.
It is very important to completely dry the plate before observing the spots with the help of an oxidizing agent even when a slight amount of alcohol is there in the mixture of solvent. If the plates are not dried completely, then oxidation of the alcohol would take place by the oxidizing agent and it will get converted to carboxylic acid or ketone, which will eventually give rise to a new spot.