International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

Which of the following indicates a neutral pH?

1. 1-3

2. 4-6

3. 7

4. 8-10

The correct answer is: 7

A neutral pH is defined as 7 on the pH scale, which ranges from 0 to 14. In pure water, at 25°C (77°F), the concentration of hydrogen ions ([H⁺]) is equal to that of hydroxide ions ([OH⁻]), resulting in a pH of 7. This represents a balance, where the solution is neither acidic (lower than 7) nor basic (higher than 7). Options representing a pH of 1-3 indicate a strongly acidic environment, while those ranging from 4-6 indicate mild acidity. Similarly, a pH of 8-10 suggests a basic (alkaline) solution. Since these ranges deviate from the neutral point, they highlight the characteristic of either acidity or alkalinity rather than neutrality. Therefore, 7 is the definitive value indicating a neutral pH.