P-Xylene is an aromatic hydrocarbon with the formula C8H10. When it reacts with acidified potassium dichromate (K2Cr2O7) at high temperature, it undergoes an oxidation reaction, resulting in the formation of terephthalic acid (C8H6O4).

The reaction can be represented by the following equation:
p-Xylene + Acidified potassium dichromate → Terephthalic acid + Other products

Here is a detailed explanation of the reaction:

1. Oxidation of p-Xylene:
p-Xylene undergoes oxidation, where the alkyl side chain is converted to a carbonyl group. This process involves the breaking of carbon-carbon bonds and the formation of a new functional group.

2. Role of Acidified Potassium Dichromate:
The acidified potassium dichromate, commonly known as chromic acid, acts as an oxidizing agent in this reaction. It provides the necessary oxygen atoms for the oxidation process to occur.

3. Formation of Terephthalic Acid:
The oxidation of p-Xylene leads to the formation of terephthalic acid. Terephthalic acid is an important organic compound that is used in the production of polyester fibers and plastic bottles.

4. No Reaction with Benzoic Acid or Phthalic Acid:
The options provided in the question, benzoic acid and phthalic acid, are not the products of the given reaction. Benzoic acid is obtained when benzyl group attached to a benzene ring is oxidized. Phthalic acid is formed by the oxidation of ortho-xylene or naphthalene.

In conclusion, when p-Xylene reacts with acidified potassium dichromate at high temperature, it undergoes oxidation to form terephthalic acid. No reaction occurs to produce benzoic acid or phthalic acid.