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If a stable neutral atom has a mass number of 31, the number of electrons...

Chemistry
JAMB 2024

If a stable neutral atom has a mass number of 31, the number of electrons and neutrons respectively are

  • A. 15 and 16
  • B. 16 and 31
  • C. 15 and 31
  • D. 16 and 15
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Correct Answer: Option A
Explanation

The only information we are given is the mass number, so we have to work our answer from the options.

Using the elimination method, options B and C are incorrect because when you add the numbers together, they give 47 and 46 respectively which is more than 31.

We are left with options A and D. However, the correct answer will be option A, since there are 15 electrons which invariably means, we also have 15 number of protons. 

⇒ The element has atomic number of 15 (Phosphorus)

There is an explanation video available below.


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Explanation Video

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Post-UTME Past Questions - Original materials are available here - Download PDF for your school of choice + 1 year SMS alerts
Post-UTME Past Questions - Original materials are available here - Download PDF for your school of choice + 1 year SMS alerts
Post UTME Past Questions Agent
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