Question 67:
Of the following pH values, which one is the lowest?
pH 0 represents the lowest value among the given options, as the pH scale is logarithmic where lower numbers indicate higher acidity and thus lower pH. This basic chemistry question tests understanding of the pH scale’s inverse relationship to hydrogen ion concentration.
Option Analysis
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(A) 0: Correct and lowest. pH 0 means [H⁺] = 1 M, the most acidic in standard aqueous scale (0-14), with each unit drop multiplying acidity by 10.
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(B) 1: Acidic but higher than 0. [H⁺] = 0.1 M, 10 times less acidic than pH 0.
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(C) 2: Less acidic still. [H⁺] = 0.01 M, 100 times less acidic than pH 0.
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(D) 7: Neutral (pure water). [H⁺] = 10⁻⁷ M, neither acidic nor basic.
pH Scale Basics
The lowest pH value indicates highest acidity on the logarithmic pH scale from 0-14, where pH = -log[H⁺]. For exams like GATE Life Sciences or chemistry, knowing pH 0 is lowest clarifies acid strength comparisons.
Why pH 0 is Lowest
pH decreases as [H⁺] rises exponentially:
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pH 0: Strongest acid here ([H⁺] = 1 mol/L).
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Each step up (1, 2) reduces acidity 10-fold.
| pH Value | [H⁺] (mol/L) | Acidity Level | Lowest? |
|---|---|---|---|
| 0 | 1 | Highest | Yes |
| 1 | 0.1 | High | No |
| 2 | 0.01 | Moderate | No |
| 7 | 10⁻⁷ | Neutral | No |
Exam Relevance
Such MCQs test scale logic for biology/chemistry competitive exams. pH 0 beats 1, 2, 7 as lowest every time.
