UPSC CDS 2 2023 GK Paper

Concept:Balancing a chemical equation ensures the same number of atoms of each element on both sides, obeying the law of conservation of mass.Explanation:We start with the unbalanced equation: $Fe + H_2O \rightarrow Fe_3O_4 + H_2$.Count atoms on each side:Left: $Fe=1$, $H=2$, $O=1$.Right: $Fe=3$, $H=2$, $O=4$.To balance Fe, place coefficient $3$ before $Fe$ on left: $3Fe + H_2O \rightarrow Fe_3O_4 + H_2$.Now Fe balanced. Next balance O: left has $1$ O, right has $4$ O. Place coefficient $4$ before $H_2O$ on left: $3Fe + 4H_2O \rightarrow Fe_3O_4 + H_2$.Now O balanced (4 on each side). Balance H: left has $4 \times 2 = 8$ H atoms; right has $2$ H atoms (from $H_2$). To balance, place coefficient $4$ before $H_2$ on right: $3Fe + 4H_2O \rightarrow Fe_3O_4 + 4H_2$.Check: Left – $Fe=3$, $H=8$, $O=4$; Right – $Fe=3$, $H=8$, $O=4$. All balanced.Answer:The balanced chemical equation is $3Fe + 4H_2O \rightarrow Fe_3O_4 + 4H_2$, which corresponds to option C.