Chemistry Question 92 – NEET-UG 2023

First, balance the Chromium atoms. The reduction half-reaction ${\text{Cr}}_2{\text{O}}_7^{2-}\to 2{\text{Cr}}^{3+}$ directly implies that the coefficient 'a' for ${\text{Cr}}_2{\text{O}}_7^{2-}$ must be 1. This immediately eliminates options (2) and (4). Then, balance the Sulfur atoms. The oxidation half-reaction ${\text{SO}}_3^{2-}\to {\text{SO}}_4^{2-}$ shows a 1:1 ratio for sulfur. The overall balancing requires 3 ${\text{SO}}_3^{2-}$ for every ${\text{Cr}}_2{\text{O}}_7^{2-}$, so $b=3$. This eliminates option (3), leaving option (1) as the correct answer.