**Correct Option: C** ### Explanation of the Correct Answer The pH scale is a measure of how acidic or basic a solution is, and it ranges from 0 to 14. Here’s a detailed breakdown of why option C is the correct answer: 1. **Understanding pH Values**: - A pH of **7** is considered **neutral**. This is the pH of pure water at 25°C (77°F). At this point, the concentration of hydrogen ions \([H^+]\) is equal to the concentration of hydroxide ions \([OH^-]\). - Values **below 7** indicate an **acidic** solution, meaning there are more hydrogen ions than hydroxide ions. For example, lemon juice has a pH around 2, indicating it is acidic. - Values **above 7** indicate a **basic (or alkaline)** solution, where there are more hydroxide ions than hydrogen ions. For instance, household bleach has a pH around 12, indicating it is basic. 2. **Why Option C is Correct**: - Option C accurately states that a pH of 7 is neutral, values below 7 indicate acidity, and values above 7 indicate alkalinity. This aligns perfectly with the scientific understanding of the pH scale. ### Why the Other Options are Incorrect - **Option A**: "The pH scale ranges from 0 to 14, where 0 is neutral and 14 is highly acidic." - **Incorrect Reasoning**: This statement incorrectly defines the endpoints of the pH scale. While it is true that the pH scale ranges from 0 to 14, it mislabels 0 as neutral and 14 as highly acidic. In reality, 0 is highly acidic, and 14 is highly basic. - **Option B**: "A pH value below 7 indicates a basic solution, while a pH value above 7 indicates an acidic solution." - **Incorrect Reasoning**: This option reverses the definitions of acidic and basic solutions. A pH below 7 indicates acidity, while a pH above 7 indicates basicity. Therefore, this statement is fundamentally incorrect. - **Option D**: "The pH scale is logarithmic, meaning each whole number change on the scale represents a tenfold change in acidity or basicity." - **Partially Correct but Incomplete**: While it is true that the pH scale is logarithmic, this option does not provide a complete description of the pH scale itself. It fails to mention the neutral point (pH 7) and the definitions of acidic and basic solutions. Thus, while it contains a true statement, it does not fully address the question. ### Summary of Key Points - The pH scale ranges from 0 to 14, with 7 being neutral (pure water). - A pH below 7 indicates acidity, while a pH above 7 indicates basicity. - The scale is logarithmic, meaning each whole number change represents a tenfold change in hydrogen ion concentration. - Understanding the pH scale is crucial for various applications in chemistry, biology, and environmental science. This thorough understanding of the pH scale will help you in both theoretical and practical aspects of chemistry.