The quantity of electricity in Faraday, required to reduce $1\text{ mol}$ of $\text{Cr}_2\text{O}_7^{2-}$ to $\text{Cr}^{3+}$ is : (A) $4\text{F}$ (B) $3\text{F}$ (C) $6\text{F}$ (D) $5\text{F}$