Product C of the following reaction sequence will be:

To determine the major product [C], we analyze the reaction sequence step by step starting from aniline.

Aniline undergoes rapid electrophilic aromatic substitution with bromine water because the $$-NH_2$$ group strongly activates the benzene ring. Bromination occurs at both ortho positions and the para position, producing 2,4,6-tribromoaniline as product [A].

On treatment with $$NaNO_2/HCl$$ at $$273\text{-}278\ \text{K}$$, the amino group of 2,4,6-tribromoaniline is converted into a diazonium group through the diazotization reaction, giving 2,4,6-tribromobenzenediazonium chloride as intermediate [B].

The diazonium salt then reacts with $$HBF_4$$ to form the corresponding diazonium fluoroborate. Subsequent treatment with $$NaNO_2$$ and copper replaces the diazonium group with a nitro group, yielding the final product

$$\text{2,4,6-tribromobenzenediazonium salt} \longrightarrow \text{1,3,5-tribromo-2-nitrobenzene}.$$

Thus, the major product [C] is 1,3,5-tribromo-2-nitrobenzene.

Hence, the correct answer is 1,3,5-tribromo-2-nitrobenzene, which corresponds to option B.