The reagent ‘R’ in the given sequence of chemical reaction is: (See structure on image page 1)

The conversion of benzene diazonium chloride (\( \text{C}_6\text{H}_2\text{Br}_3\text{N}_2^+\text{Cl}^- \)) to tribromobenzene involves replacing the diazonium group with hydrogen. This is reductive deamination achieved using \( \text{CH}_3\text{CH}_2\text{OH} \) (ethanol) or hypophosphorous acid.