Which of the following chemical equations is correctly balanced?

• A. H_2 + O_2 ightarrow H_2O
• B. 2 H_2 + O_2 ightarrow 2 H_2O
• C. 2 H_2 + 2 O_2 ightarrow 2 H_2O
• D. H_2 + 2 O_2 ightarrow 2 H_2O

Answer: (B)

Verified step by step guidance

1. Identify the chemical species involved in the reaction: hydrogen gas (\(\mathrm{H_2}\)) and oxygen gas (\(\mathrm{O_2}\)) react to form water (\(\mathrm{H_2O}\)).
2. Write the unbalanced chemical equation: \(\mathrm{H_2 + O_2 \rightarrow H_2O}\).
3. Count the number of atoms of each element on both sides of the equation. On the reactant side, there are 2 hydrogen atoms and 2 oxygen atoms; on the product side, there are 2 hydrogen atoms and 1 oxygen atom.
4. Balance the oxygen atoms by adjusting the coefficients. Since oxygen appears as \(\mathrm{O_2}\) on the left and as a single oxygen atom in \(\mathrm{H_2O}\) on the right, multiply \(\mathrm{H_2O}\) by 2 to have 2 oxygen atoms on the product side: \(\mathrm{H_2 + O_2 \rightarrow 2 H_2O}\).
5. Balance the hydrogen atoms by adjusting the coefficient of \(\mathrm{H_2}\) on the reactant side. Since there are 4 hydrogen atoms on the product side (from \$2 \times \mathrm{H_2O}\(), multiply \)\mathrm{H_2}\( by 2: \)\mathrm{2 H_2 + O_2 \rightarrow 2 H_2O}$. This equation is now balanced.