PSI Barbering Practice Exam

Which molecule is formed when hydrogen and oxygen combine during a reaction?

1. Water

2. Hydroxide

3. Hydrogen Peroxide

4. Ozone

The correct answer is: Water

When hydrogen and oxygen combine during a chemical reaction, they form water. This is a fundamental reaction in chemistry, known as the combustion of hydrogen, which can be represented by the equation: 2 H₂ (g) + O₂ (g) → 2 H₂O (l) In this reaction, two molecules of diatomic hydrogen gas react with one molecule of diatomic oxygen gas to yield two molecules of liquid water. Water is a stable compound that consists of two hydrogen atoms covalently bonded to one oxygen atom, which is essential for life and plays a crucial role in various biological and chemical processes. The other options present different compounds that do not result directly from the straightforward combination of hydrogen and oxygen. Hydroxide, for example, refers to the anion OH⁻, which is a component of bases but is not directly formed from the reaction between molecular hydrogen and oxygen. Hydrogen peroxide contains two hydrogen atoms and two oxygen atoms but is formed through a different reaction pathway. Ozone consists of three oxygen atoms and does not involve hydrogen in its formation, making it unrelated to the direct combination of hydrogen and oxygen.