# DBT JRF 2022 — Question 5

Exam: DBT JRF 2022 · Section: B · Topic: Biochemistry › Molecular Weight of Organic Compounds · Difficulty: Medium

## Question

What, if any, is the difference between the molecular weights of molecule A (left) vs molecule B (right)? ![figure](https://res.cloudinary.com/dxil5euku/image/upload/v1779453123/pyq/6a104cb5920734408bc0c6d8/DBTJRF22-IMGB5.png)

## Options

- **A.** Molecular weight of the two are identical
- **B.** Molecular weight of A is less by 20 Daltons
- **C.** Molecular weight of A is more by 14 Daltons
- **D.** Molecular weight of B is more by 2 Daltons

## Answer

Option C

## Explanation

Molecular weight difference between molecule A and B ![figure](https://res.cloudinary.com/dxil5euku/image/upload/v1779453123/pyq/6a104cb5920734408bc0c6d8/DBTJRF22-IMGB5.png) : Comparing the two molecular structures in the image: • Molecule A has one additional $-\text{CH}_2-$ group compared to Molecule B. • Molecular weight of a $-\text{CH}_2-$ group = 12 (C) + 2×1 (2H) = 14 Da. Therefore, Molecule A is more massive by 14 Daltons than Molecule B. Answer: Molecular weight of A is more by 14 Daltons (Option 3).

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