Find the total number of halogen atoms present in the major end product

The total number of halogen atoms in the major end product is 3.

Detailed Solution:

1. The starting compound is 1,4-dinitrobenzene.
2. In the first step, with NH₄HS, one nitro group (-NO₂) is converted to an amino group (-NH₂), forming P (1-amino-4-nitrobenzene).
3. In the second step, bromine water (Br₂/H₂O) reacts, substituting bromine atoms at the ortho- and para-positions relative to the amino group, forming Q (2,6-dibromo-4-nitroaniline).
4. In the third step, diazotization (NaNO₂/HCl) converts the amino group to a diazonium group (-N₂⁺), forming R (2,6-dibromo-4-nitrobenzenediazonium).
5. In the final step, Sandmeyer reaction (CuBr/HBr) replaces the diazonium group with a bromine atom, forming the major end product: 2,4,6-tribromonitrobenzene.
6. The major product contains 3 bromine atoms.

Concept Behind the Problem:

This problem is based on understanding the sequence of reactions:

• Reduction: Converting -NO₂ to -NH₂.
• Bromination: Adding bromine to positions ortho and para to -NH₂.
• Diazotization: Converting -NH₂ to -N₂⁺.
• Sandmeyer Reaction: Replacing -N₂⁺ with a halogen atom.

The final product is identified based on the substitution reactions and their regioselectivity.