# DBT JRF 2020 — Question 11

Exam: DBT JRF 2020 · Section: A · Topic: Biochemistry · Difficulty: Medium

## Question

Someone tells you that the pH of a solution is minus 2. Which one of the following is false?

## Options

- **A.** such a value of pH is unlikely to occur in practice
- **B.** such a value of pH is impossible even in theory
- **C.** concentration of $H_3O^+$ is 100 M
- **D.** such a value of pH is possible in theory

## Answer

Option B

## Explanation

$\text{pH} = -\log_{10}[\text{H}^+]$ , so $\text{pH} = -2$ implies $[\text{H}^+] = 10^2 = 100 \text{ M}$ . Since pure water is ~55.5 M, a 100 M solution of $\text{H}^+$ is physically impossible in aqueous solution. However, pH is simply a mathematical function $(-\log[\text{H}^+])$ and is not restricted to positive values by theory — it is possible mathematically (theoretically). The statement 'such a value of pH is impossible even in theory' is therefore FALSE. In practice, the pH scale is limited to ~0–14 for dilute aqueous solutions.

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