Chemistry Electrochemistry NUMS 2024
PMDC Verified Question 17 of 73
Zn rod acts as cathode when coupled with magnesium electrode. This is because the reduction potential of:
A
Zn > Mg
B
Fe is precipitated out
C
Cu and Fe both dissolve
D
No reaction taken place
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option A: Zn > Mg
Concept:

In a galvanic cell, the electrode composed of the metal with the higher (more positive/less negative) standard reduction potential acts as the cathode.

Solution:

  • The standard reduction potential of Zinc (\( Zn \)) is \( -0.76 \text{ V} \).


  • The standard reduction potential of Magnesium (\( Mg \)) is \( -2.37 \text{ V} \).


  • Because \( -0.76 \text{ V} \) is mathematically greater than \( -2.37 \text{ V} \) (Zn > Mg), Zinc has a stronger thermodynamic pull on electrons.


  • Zinc forces Magnesium to oxidize (act as the anode), while Zinc undergoes reduction (acts as the cathode).


Why other options are incorrect:

Note: Options B, C, and D are physical misprints in the original source book, accidentally copied from the subsequent question. The only chemically relevant and correct answer is A.

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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