The following statements are given about the pH scale:
Assertion: A solution with pH = 12 is strongly basic.
Reason: As pH increases above 7, the concentration of OH⁻ ions increases in the solution.
Both assertion and reason are correct and the reason correctly explains the assertion. Do you agree? Justify.
Generated by claude-sonnet-4-6 · 2026-06-17 12:38 · grounding rag
Model Answer
Yes, I agree. Both the assertion and reason are correct, and the reason correctly explains the assertion.
A solution with pH = 12 is far above 7, which indicates it is strongly basic. According to the pH scale, as the pH value increases from 7 to 14, it represents an increase in OH⁻ ion concentration in the solution, meaning greater alkaline strength. Therefore, pH = 12 corresponds to a high concentration of OH⁻ ions, making it strongly basic. The reason directly and correctly explains the assertion.
Source: Chapter 2, Section 2.3 – How Strong Are Acid or Base Solutions?
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Explanation
- CBSE Assertion-Reason questions at this level ask you to confirm the relationship, not just label it.
- Key textbook line to quote/paraphrase: "As the pH value increases from 7 to 14, it represents an increase in OH⁻ ion concentration."
- Always link the reason back to the assertion explicitly — examiners check that you explain how the reason justifies the assertion, not just that both are true.
- pH = 12 is strongly (not weakly) basic because it is close to 14, far above 7.