The number of terminal oxygen atoms present in the product B obtained from the following reaction is \ \ \ \. FeCr_2 O_4+ Na_2 CO_3+ O_2 → A + Fe_2…

The number of terminal oxygen atoms present in the product B obtained from the following reaction is \_\_\_\_. $$\begin{aligned} & \mathrm{FeCr}_2 \mathrm{O}_4+\mathrm{Na}_2 \mathrm{CO}_3+\mathrm{O}_2 \rightarrow \mathrm{~A}+\mathrm{Fe}_2 \mathrm{O}_3+\mathrm{CO}_2 \\ & \mathrm{~A}+\mathrm{H}^{+} \rightarrow \mathrm{B}+\mathrm{H}_2 \mathrm{O}+\mathrm{Na}^{+} \end{aligned} $$