The reaction between Cr₂O₇^2- and HNO₃ in an acidic medium is 

Cr₂O₇^2- + 5H⁺ + 3HNO₂ → 2Cr³⁺ + 3NO₃^- + 4H₂O

The rate of reaction is found to be 2.4 x 10^-4 mol L^-1 s^-1, during the measured time interval. Find the rate of disappearance of HNO₂.

7.2 x 10^-4 mol L^-1 s^-1   

Rate  = 2.4 x 10^-4 mol L^-1 s^-1 

-\(\frac{d[HNO_2]}{dt}\) = 3 x (2.4 x 10^-4) = 7.2 x 10^-4 mol L^-1 s^-1