The mass of iron converted into \( \mathrm{Fe_3O_4} \) by the action of \( 18 \, \text{g} \) of steam is:(Given: Molar mass of H, O and Fe are \( 1 \), \( 16 \) and \( 56 \, \text{g mol}^{-1} \) respectively)Assume iron is present in excess:
\( 2.1 \, \text{g} \)
\( 4.2 \, \text{g} \)
\( 21 \, \text{g} \)
\( 42 \, \text{g} \)
