A student adds $3$ mol of acidified $\text{K}_2\text{Cr}_2\text{O}_7$ to an excess of $\text{I}^-$ ions. All the chromium is reduced completely to $\text{Cr}^{3+}$, while the $\text{I}^-$ ions are oxidised to $\text{I}_2$. The $\text{I}_2$ formed is then reduced back to $\text{I}^-$ by $X$ mol of $\text{S}_2\text{O}_3^{2-}$ ions. $1$ mol of $\text{I}_2$ is reduced by $2$ mol of $\text{S}_2\text{O}_3^{2-}$ ions. What is the value of $X$?
- A$3$
- B$6$
- C$9$
- D$18$