Chemistry Atomic Structure MDCAT 2014
PMDC Verified Question 90 of 95
According to the number of protons, neutrons and electrons given in the table, which one of the following options is correct?

SpeciesProtonNeutronElectron
As334230
Ga313928
Ca202020
A
\( \text{As}^{+3}, \text{Ga}, \text{Ca}^{-2} \)
B
\( \text{As}^{+3}, \text{Ga}^{+3}, \text{Ca}^{+2} \)
C
\( \text{As}^{+3}, \text{Ga}^{+3}, \text{Ca} \)
D
\( \text{As}^{+3}, \text{Ga}^{+2}, \text{Ca} \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: \( \text{As}^{+3}, \text{Ga}^{+3}, \text{Ca} \)
Concept: The charge of an ion is determined by the difference between its protons (positive charge) and electrons (negative charge).

Formula: $$ \text{Charge} = \text{Protons} - \text{Electrons} $$

Solution:
  • For As: \( 33 - 30 = +3 \implies \text{As}^{+3} \)
  • For Ga: \( 31 - 28 = +3 \implies \text{Ga}^{+3} \)
  • For Ca: \( 20 - 20 = 0 \implies \text{Ca}^0 \) (Neutral atom)


Why other options are incorrect: They assign incorrect charges, such as giving Calcium a charge when its protons and electrons are equal.

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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