Correct answer: B. Increases

In the Sephadex G series (G‑10, G‑15, G‑25 … G‑200), a higher G number corresponds to a higher molecular weight exclusion limit, which in practice means larger internal pores in the gel beads. As the G number increases, the beads can accommodate and separate larger molecules, so the effective pore size increases.

Why option B is correct (pore size increases)

• Sephadex is a cross‑linked dextran gel used for gel filtration (size exclusion) chromatography.

• The G number (e.g., G‑10, G‑25, G‑100) is related to the exclusion limit of the gel in terms of molecular weight; higher G numbers can separate larger molecules.

• To allow larger molecules into the beads, the internal pores must be larger, so as you go from G‑10 to G‑200, the pore size increases.

• Therefore, as the G number increases, the pore size of the beads increases, making B the correct answer.

Why option A is incorrect (pore size decreases)

• If pore size decreased, the gel would exclude larger and larger molecules and only allow very small molecules inside.

• That would mean higher G numbers are suitable only for smaller molecules, which is the opposite of what is observed in Sephadex gels.

• Hence, saying pore size decreases with increasing G number contradicts the basic design and labeling of the Sephadex G series.

Why option C is incorrect (pore size remains constant)

• Different Sephadex G types are specifically manufactured to have different fractionation ranges, which depend directly on pore size.

• If pore size were constant, G‑10, G‑25, G‑50, G‑100, G‑200 would all separate the same range of molecular weights, making the series meaningless.

• Therefore, pore size cannot remain constant across the series.

Why option D is incorrect (varies from manufacturer to manufacturer)

• Sephadex is a trademarked, standardized product line (originally from Pharmacia/GE/Cytiva), with well‑defined G numbers and corresponding fractionation ranges.

• While minor batch-to-batch differences can exist in any material, the trend of increasing pore size with higher G number is fixed, not arbitrarily varying between manufacturers.

• So the systematic relationship between G number and pore size is not manufacturer dependent in the way option D suggests.

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Introduction (SEO‑Optimized)

Sephadex G series pore size is a fundamental concept in gel filtration chromatography for separating biomolecules by size. Understanding how pore size changes with G number, from G‑10 up to G‑200, helps you choose the right Sephadex grade for protein and polysaccharide purification as well as solve competitive exam questions accurately.

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What Is the Sephadex G Series?

Sephadex is a cross‑linked dextran gel commonly used in size exclusion chromatography. Different G types (G‑10, G‑15, G‑25, G‑50, G‑75, G‑100, G‑200) are designed to separate molecules over distinct molecular weight ranges.

Key points:

• Each G number corresponds to an approximate molecular weight exclusion limit.

• Lower G numbers (e.g., G‑10, G‑15) are for very small molecules.

• Higher G numbers (e.g., G‑100, G‑200) are for larger molecules, such as bigger proteins and polysaccharides.

• This behavior is directly linked to the pore size of the beads.

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Relationship Between G Number and Pore Size

As you move from G‑10 → G‑15 → G‑25 → … → G‑200, the gels are designed with progressively larger pores.

• Higher G number → higher exclusion limit → larger pores.

• Larger pores allow entry of larger solute molecules into the bead interior.

• This expands the fractionation range, enabling separation of higher molecular weight species.

A simple way to think of it:

• G‑10: small pores, only very small molecules can enter.

• G‑25 / G‑50: medium pores, suitable for many peptides and small proteins.

• G‑100 / G‑200: large pores, suitable for larger proteins and polysaccharides.

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Concept Check: MCQ Recap

To reinforce the concept:

As the G number increases from 10, 15, 25 … 200, the pore size of the beads:

• A. Decreases

• B. Increases ✅

• C. Remains constant

• D. Varies from manufacturer to manufacturer

Because higher G numbers are designed for higher molecular weight exclusion limits, the Sephadex G series pore size increases with G number, making option B correct.

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Summary Table: G Number vs Pore Logic

(Exact numerical ranges vary by datasheet, but the trend of increasing pore size with increasing G number is fixed.)

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This structure gives you both a clear conceptual understanding for exams and an SEO‑friendly article targeting the key phrase “Sephadex G series pore size.”