The equilibrium $\mathrm{Cr}_2 \mathrm{O}_7^{2-} \rightleftharpoons 2 \mathrm{CrO}_4^{2-}$ is shifted to the right in :

<p>The equilibrium $\mathrm{Cr}_2 \mathrm{O}_7^{2-} \rightleftharpoons 2 \mathrm{CrO}_4^{2-}$ can be influenced by changes in the pH of the medium, according to Le Chatelier's principle. This principle states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change.</p> <p>In this case:</p> <p>$\mathrm{Cr}_2 \mathrm{O}_7^{2-}$ is dichromate, which exists more prominently in acidic conditions. On the other hand, $\mathrm{CrO}_4^{2-}$ is chromate, which is favored in basic conditions. When the medium is basic, hydrogen ion concentration decreases, leading to the formation of more chromate ions ($\mathrm{CrO}_4^{2-}$).</p> <p>Thus, in a basic medium, the reaction shifts to the right, resulting in the formation of $2 \mathrm{CrO}_4^{2-}$ from $\mathrm{Cr}_2 \mathrm{O}_7^{2-}$.</p> <p>Therefore, the correct option is:</p> <p><b>Option B: a basic medium</b></p>