# DBT JRF 2022 — Question 14

Exam: DBT JRF 2022 · Section: B · Topic: Biochemistry › Spectrophotometry - Beer-Lambert Law · Difficulty: Medium

## Question

What will be the absorbance of a 1 mM solution of molecule X whose molar extinction coefficient is 1000 $M^{-1}cm^{-1}$ & path length of the cuvette used is 1 cm?

## Options

- **A.** 1.0
- **B.** 0.1
- **C.** 0.5
- **D.** 2.0

## Answer

Option A

## Explanation

Beer-Lambert Law — absorbance calculation: The Beer-Lambert Law states: $A = \varepsilon \cdot c \cdot l$ where: • $A$ = absorbance (dimensionless) • $\varepsilon$ = molar extinction coefficient (M⁻¹cm⁻¹) = 1000 M⁻¹cm⁻¹ • $c$ = concentration = 1 mM = $1 \times 10^{-3}$ M • $l$ = path length of cuvette = 1 cm Calculation: $A = 1000 \times 10^{-3} \times 1 = 1.0$ Note: The extinction coefficient $\varepsilon$ has units M⁻¹cm⁻¹, so units cancel: $(\text{M}^{-1}\text{cm}^{-1}) \times \text{M} \times \text{cm} =$ dimensionless. Answer: Absorbance = 1.0 (Option 1).

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