Which term best describes the role of hydrogen gas in the formation of a water molecule?

• A. Product
• B. Reactant
• C. Catalyst
• D. Solvent

Answer: (B)

Verified step by step guidance

1. Identify the substances involved in the chemical reaction forming water. Hydrogen gas (H\_2) and oxygen gas (O\_2) combine to form water (H\_2O).
2. Understand the definitions of the terms: A reactant is a substance that undergoes change during a chemical reaction; a product is the substance formed as a result of the reaction; a catalyst speeds up the reaction without being consumed; a solvent is a medium in which reactions occur but does not react itself.
3. Since hydrogen gas is consumed and chemically changes to form water, it fits the definition of a reactant.
4. Confirm that hydrogen gas is not a product because it is not formed by the reaction, nor is it a catalyst or solvent because it participates directly in the reaction.
5. Therefore, the best term to describe the role of hydrogen gas in the formation of water is 'Reactant'.