Question

In acidic medium, the rate of reaction between $\left[Br{O}_3^{-}\right]$ and $\left[B{r}^{-}\right]$ ions is given by the expression $-\frac{d\left[Br{O}_3^{-}\right]}{dt}=k\left[Br{O}_3^{-}\right]\left[B{r}^{-}\right][H^{+}{]}^2$
It means:
(i) Rate constant of the reaction depends upon the concentration of $H^{+}$ ions
(ii) Rate of reaction is independent of the concentration of acid added
(iii) The change in $pH$ of the solution will affect the rate of reaction
(iv) Doubling the concentration of $H^{+}$ ions will increase the reactions rate by $4$ times.

• A. Only (ii)
• B. Only (iii)
• C. Only (i) and (ii)
• D. Only (iii) and (iv)

Answer 1

The correct option is D Only (iii) and (iv)

(i) is wrong because rate constant does not depend upon the concentrations of the reactants.
(ii) is wrong because rate depends upon $[H^{+}{]}^2$
(iii) is correct because change in $pH$ means change in $\left[H^{+}\right]$ ions
(iv) is correct because rate $\propto [H^{+}{]}^2$.