Chemistry Atomic Structure MDCAT 2017
PMDC Verified Question 81 of 95
Isotopic symbol of ion of Sulphur-33 is \( ^{33}_{16}\text{S}^{-2} \). How many numbers of protons and neutrons are present if number of electrons are 18?
A
\( P = 18, n = 15 \)
B
\( P = 16, n = 18 \)
C
\( P = 16, n = 17 \)
D
\( P = 17, n = 16 \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: \( P = 16, n = 17 \)
Concept: Protons are strictly determined by the atomic number (\(Z\)), and neutrons are determined by mass number (\(A\)) minus atomic number (\(Z\)), regardless of the electron count.

Formula: $$ P = Z $$ $$ N = A - Z $$

Solution:
  • The symbol \( ^{33}_{16}\text{S}^{-2} \) gives \( Z = 16 \) (subscript) and \( A = 33 \) (superscript).
  • Number of protons \( (P) = Z = 16 \).
  • Number of neutrons \( (n) = A - Z = 33 - 16 = 17 \).


Why other options are incorrect: They confuse the electron count (18) with the proton or neutron counts, which are fixed by the nucleus.

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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