Reduction is defined as the acceptance of electrons. The provided reaction is depicted as:\[\mathrm{Cr^{3+} + 3e^- \rightarrow Cr^0}.\]Based on this reaction: It takes 3 electrons (\( 3e^- \)) for each \( \mathrm{Cr^{3+}} \) ion to achieve reduction to \( \mathrm{Cr^0} \). Consequently, 3 moles of electrons are necessary for 1 mole of \( \mathrm{Cr^{3+}} \).Key Information: The oxidation state of chromium transitions from \( +3 \) in \( \mathrm{Cr^{3+}} \) to \( 0 \) in \( \mathrm{Cr^0} \). The quantity of moles of electrons needed corresponds directly to the magnitude of the change in oxidation state.Hence, the required quantity is \( \mathbf{3 \, \text{moles of} \, e^-} \).