The major product formed in the following reaction is

Explanation:

The conversion of 4-nitrobenzoic acid to 4-aminobenzoic acid in the presence of hydrogen gas (H₂), Raney nickel (Ni), and at room temperature (RT) involves a reduction reaction. The mechanism for this reaction can be explained as follows:

1. Adsorption of H₂ on the surface of Raney Nickel (Ni): The first step involves the adsorption of hydrogen gas on the surface of Raney Nickel. Raney Nickel is a highly porous form of nickel that provides a large surface area for the adsorption of H2 molecules.

2. Formation of Ni-H bond: The adsorbed hydrogen atoms interact with the nickel surface, forming Ni-H bonds. This step generates highly reactive Ni-H species, which will be used to reduce the nitro group.

3. Formation of a complex between 4-nitrobenzoic acid and Ni: The next step involves the interaction of 4-nitrobenzoic acid with the Ni-H complex, leading to the formation of a complex between the two species.

4. Reduction of the nitro group: In the presence of the Ni-H complex, the nitro group in the 4-nitrobenzoic acid is reduced to an amino group. The hydrogen atoms from the Ni-H complex are added to the nitro group, generating water as a byproduct.

5. Desorption of the product: Finally, the product, 4-aminobenzoic acid, is desorbed from the surface of the catalyst. The catalyst can be reused for further reactions.

Mechanism:

Conclusion: 
Overall, the reduction of 4-nitrobenzoic acid to 4-aminobenzoic acid in the presence of H₂ and Raney Nickel involves a complex mechanism that requires the adsorption of hydrogen gas, the formation of a complex between the substrate and the catalyst, and the reduction of the nitro group by the Ni-H complex.