Chemistry Chemical Bonding MDCAT 2017
PMDC Verified Question 89 of 102
Observe the given dot and cross structures for the following molecules or ionic species. The co-ordinate covalent bond exists between:

N H H H
A
N and C atoms in structure III and IV
B
N and one H ion in all four structure
C
N and Cl atoms of structure II
D
N and N atoms of structure I
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: N and one H ion in all four structure
Concept:

A coordinate covalent (dative) bond forms when one atom provides both electrons for a shared pair.

Formula:

$$ \text{NH}_3 + \text{H}^+ \longrightarrow \text{NH}_4^+ $$

Solution:

  • In all four illustrated structures, the core species is the ammonium ion (\( \text{NH}_4^+ \)).


  • The nitrogen atom in ammonia (\( \text{NH}_3 \)) has one lone pair.


  • Nitrogen donates this lone pair to an empty 1s orbital of a hydrogen ion (\( \text{H}^+ \)), forming a coordinate covalent bond between N and H.


Why other options are incorrect:

  • Option A, C & D: These do not accurately describe the dative bond formation, which exclusively occurs between the central Nitrogen and the incoming Hydrogen ion.

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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