The number of terminal oxygen atoms present in the product \( B \) obtained from the following reaction is __________.
\( \mathrm{FeCr_2O_4 + Na_2CO_3 + O_2 \rightarrow A + Fe_2O_3 + CO_2} \)
\( A + \mathrm{H^+} \rightarrow B + \mathrm{H_2O} + \mathrm{Na^+} \)
