# DBT JRF 2020 — Question 78

Exam: DBT JRF 2020 · Section: B · Topic: Biochemistry · Difficulty: Easy

## Question

What will be the molarity of a 4 mg/ml solution of NaOH?

## Options

- **A.** 0.1 M
- **B.** 4 M
- **C.** 0.0844 M
- **D.** 1 M

## Answer

Option A

## Explanation

Molarity calculation for NaOH: $M_r(\text{NaOH}) = 23(\text{Na}) + 16(\text{O}) + 1(\text{H}) = 40 \text{ g/mol}$ . Given: 4 mg/mL = 4 g/L (since 1 mg/mL = 1 g/L). $\text{Molarity} = \dfrac{\text{mass (g/L)}}{M_r (\text{g/mol})} = \dfrac{4}{40} = 0.1 \text{ mol/L} = 0.1 \text{ M}$ .

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