OCR A-Level Chemistry AS Breadth in chemistry (01), June 2024: Question 2

1 mark · Easy difficulty · Multiple Choice

Determine the number of protons, neutrons, and electrons in the magnesium ion 25Mg2+.

Practise this question

Question

Multiple choice question 2 asking which row shows the atomic structure of 25Mg2+, with a table containing four rows labeled A to D, detailing numbers of protons, neutrons, and electrons.
Question text

2 Which row shows the atomic structure of 25Mg2+?

Protons Neutrons Electrons

A 10 12 13

B 10 15 12

C 12 13 10

D 12 13 14

Your answer [1]

Mark scheme

Show the mark scheme The mark scheme indicates that the correct answer for question 2 is C, worth 1 mark.

2 C 1

How to answer it

Atomic Structure of ⁨²⁵Mg²⁺⁩

What this question tests

This question assesses your ability to determine the number of fundamental subatomic particles (protons, neutrons, and electrons) in an isotope given its mass number, atomic number, and ionic charge.

Question Multiple Choice Analysis

Part 1: Identifying the Subatomic Particles

✅ Correct Answer: C

Row C correctly identifies protons as 12, neutrons as 13, and electrons as 10.

💡 Key Knowledge

  • Protons: Given by the atomic number of magnesium (Z = 12).
  • Neutrons: Calculated by Mass Number minus Atomic Number ( 25 - 12 = 13 ).
  • Electrons: For a neutral atom, electrons equal protons (12). The 2+ charge means 2 electrons have been lost ( 12 - 2 = 10 ).

🧠 Exam Technique

Work out each particle one by one and eliminate rows systematically. Start with protons since they define the element. Then look at the ion charge to easily isolate the correct electron count.

❌ Common Errors

Students often forget to adjust the electron count for the ionic charge (selecting Row D because they assume a neutral 12 electrons), or they confuse mass number with neutron count.

Mark Scheme Award: 1 mark for selecting option C.

Topics

Module 2: Foundations in chemistry · 2.1 Atoms and reactions

Question and mark scheme from the OCR A-Level Chemistry examination, AS Breadth in chemistry (01), June 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.