The correct option is A 4
A balanced chemical equation has an equal number of atoms of each element in reactants and products.
Consider the coefficients of Fe as 'A', H2O as 'B', Fe3O4 as 'C' and H2 as 'D'.
Given, A = 3, C = 1 and D = 4
By shortcut method, 2B = 2D
2B = 2×4
⟹B = 4
Since, B = x Therefore, x = 4