If pH changes from 4 to 7, what happens to the hydrogen-ion concentration?
Answer and explanation
Correct answer: It decreases one thousandfold
The pH scale is logarithmic, and pH = −log[H⁺]. Therefore, an increase of one pH unit means a tenfold decrease in hydrogen-ion concentration. The change from pH 4 to pH 7 is three units, so the concentration changes by 10³ = 1000 times in the decreasing direction. Hence option C is correct; the other numerical options do not apply the logarithmic scale correctly.
Frequently asked questions
What is the correct answer to this question?
It decreases one thousandfold
Why is this the correct answer?
The pH scale is logarithmic, and pH = −log[H⁺]. Therefore, an increase of one pH unit means a tenfold decrease in hydrogen-ion concentration. The change from pH 4 to pH 7 is three units, so the concentration changes by 10³ = 1000 times in the decreasing direction. Hence option C is correct; the other numerical options do not apply the logarithmic scale correctly.
Which subject and chapter does this question cover?
This is a Class 10 Science question. Chapter: Chemical Substances – Nature and Behaviour. Topic: Acids, Bases, and Salts.
