Question 31:
Which one of the following i.e., number of molecules per gram molecular weight, represents the Avogadro’s number (N)?
Avogadro’s number is the count of molecules (or atoms, ions) in one gram molecular weight, which is precisely 6.02 × 10²³. The correct answer is option (C).
Question Breakdown
This multiple-choice question tests the fundamental definition of Avogadro’s number (N_A), a key constant in chemistry for one mole of substance.
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Option (A) 6.02 × 10⁶: Too small; equals about 6 million particles, akin to cells in a human body, not a mole’s scale.
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Option (B) 6.02 × 10⁷: Still tiny at 60 million particles; irrelevant for molecular counting in chemistry.
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Option (C) 6.02 × 10²³: Correct; exactly matches Avogadro’s number, particles per gram molecular weight (one mole).
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Option (D) 6.02 × 10³³: Excessively large; no chemical constant fits this magnitude.
Introduction
Avogadro’s number (N), defined as 6.02 × 10²³ molecules per gram molecular weight, is a cornerstone of chemistry for competitive exams like GATE Life Sciences. This constant links macroscopic masses to microscopic particle counts in one mole.
What is Avogadro’s Number?
Avogadro’s number (N) quantifies particles—atoms, molecules, or ions—in one gram molecular weight of a substance.
It equals exactly 6.02214076 × 10²³ mol⁻¹, though 6.02 × 10²³ suffices for most calculations.
Named after Amedeo Avogadro, it standardizes mole concepts in stoichiometry and biochemistry.
Importance in Life Sciences
In molecular biology and GATE prep, it converts grams to particle numbers for enzyme kinetics or DNA quantification.
Example: 18g water (gram molecular weight) holds 6.02 × 10²³ H₂O molecules.
| Concept | Value | Application |
|---|---|---|
| Gram Molecular Weight | Mass of 1 mole | Links to N particles |
| Avogadro’s Number (N) | 6.02 × 10²³ | Stoichiometry calculations |
| Mole | 1 gram formula mass | Exam problems in biochemistry |
