Observe the reaction sequence provided in the diagram. Identify the...

The starting material is p-tert-butyltoluene.

In the first step, the reaction with alkaline $KMnO_4$ followed by acidification ($H_3O^+$) is an oxidation of alkylbenzenes. Alkyl groups attached to a benzene ring that possess at least one benzylic hydrogen are oxidized to a carboxylic acid ($-COOH$) group.

The methyl group ($-CH_3$) has three benzylic hydrogens and is oxidized to a $-COOH$ group. The tert-butyl group ($-C(CH_3)_3$) lacks benzylic hydrogens and is resistant to oxidation. Therefore, product A is p-tert-butylbenzoic acid.

In the second step, heating product A with sodalime ($NaOH + CaO$) results in decarboxylation. The $-COOH$ group is removed as $CO_2$ (forming $Na_2CO_3$) and replaced by a hydrogen atom.

Thus, the final major product B is tert-butylbenzene.

Answer: tert-Butylbenzene