Chemistry Fundamental Principles of Organic Chemistry UHS 2023
PMDC Verified Question 20 of 83
What is the molecular formula of pyridine molecule?
A
\( \text{C}_6\text{H}_5\text{N} \)
B
\( \text{C}_5\text{H}_5\text{N} \)
C
\( \text{C}_5\text{H}_5\text{NH} \)
D
\( \text{C}_6\text{H}_6\text{N} \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: \( \text{C}_5\text{H}_5\text{N} \)
Concept:

Pyridine is a heterocyclic aromatic compound structurally related to benzene.

Solution:

  • Benzene has the molecular formula \( \text{C}_6\text{H}_6 \).


  • In pyridine, one carbon atom and its attached hydrogen atom (a \( \text{-CH-} \) group) are replaced by a single nitrogen atom (\( \text{-N=} \)).


  • Subtracting \( \text{CH} \) from \( \text{C}_6\text{H}_6 \) and adding \( \text{N} \) yields the formula \( \text{C}_5\text{H}_5\text{N} \).


Why other options are incorrect:

Option A incorrectly implies the ring has 6 carbons. Option C incorrectly adds an extra hydrogen to the nitrogen (which would disrupt the aromatic double bonds). Option D is simply incorrect atom counting.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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