### Correct Option: C. 2 H₂ + O₂ → 2 H₂O; 2:1 ### Detailed Explanation: 1. **Understanding the Reaction**: The reaction between hydrogen gas (H₂) and oxygen gas (O₂) to form water (H₂O) is a fundamental chemical reaction known as combustion. In this reaction, hydrogen and oxygen combine to produce water. 2. **Writing the Unbalanced Equation**: Initially, we can write the unbalanced equation as: \[ \text{H}_2 + \text{O}_2 \rightarrow \text{H}_2\text{O} \] 3. **Balancing the Equation**: To balance the equation, we need to ensure that the number of atoms of each element on the reactant side (left) is equal to the number on the product side (right). - **Counting Atoms**: - On the left side: - H: 2 (from H₂) - O: 2 (from O₂) - On the right side: - H: 2 (from H₂O) - O: 1 (from H₂O) - **Balancing Oxygen**: Since there are 2 oxygen atoms on the left and only 1 on the right, we need to adjust the number of water molecules produced. We can do this by placing a coefficient of 2 in front of H₂O: \[ \text{H}_2 + \text{O}_2 \rightarrow 2 \text{H}_2\text{O} \] - **Recounting Atoms**: Now, we have: - On the left: - H: 2 - O: 2 - On the right: - H: 4 (from 2 H₂O) - O: 2 (from 2 H₂O) - **Balancing Hydrogen**: To balance the hydrogen, we need 4 hydrogen atoms on the left. We can achieve this by placing a coefficient of 2 in front of H₂: \[ 2 \text{H}_2 + \text{O}_2 \rightarrow 2 \text{H}_2\text{O} \] - **Final Count**: - Left: - H: 4 (from 2 H₂) - O: 2 (from O₂) - Right: - H: 4 (from 2 H₂O) - O: 2 (from 2 H₂O) Now, the equation is balanced. 4. **Mole Ratio**: The balanced equation shows that for every 2 moles of hydrogen gas (H₂), 1 mole of oxygen gas (O₂) is required to produce 2 moles of water (H₂O). Therefore, the mole ratio of hydrogen to oxygen in this reaction is: \[ \text{Mole ratio of H₂ to O₂} = 2:1 \] ### Why Other Options Are Incorrect: - **Option A: 2 H₂ + O₂ → 2 H₂O; 1:1** - This option correctly states the balanced equation but incorrectly states the mole ratio. The correct mole ratio is 2:1, not 1:1. - **Option B: H₂ + O₂ → H₂O; 2:1** - This option presents an unbalanced equation. The correct balanced equation is 2 H₂ + O₂ → 2 H₂O. Additionally, the mole ratio stated (2:1) is correct, but it is based on an incorrect equation. - **Option D: H₂ + O₂ → 2 H₂O; 1:2** - This option also presents an unbalanced equation. The correct balanced equation is 2 H₂ + O₂ → 2 H₂O. The mole ratio of 1:2 is incorrect; it should be 2:1. ### Revision Summary: - The balanced chemical equation for the reaction of hydrogen and oxygen to form water is **2 H₂ + O₂ → 2 H₂O**. - The mole ratio of hydrogen to oxygen in this reaction is **2:1**. - Always ensure to balance chemical equations by counting the number of atoms of each element on both sides. - Use coefficients to adjust the number of molecules in the reaction to achieve balance.