AQA A-Level Chemistry AS Paper 1, June 2023: Question 9

1 mark · Easy difficulty · Multiple Choice

Identify which atom contains the greatest number of neutrons from a given list of isotopes.

Practise this question

Question

Question 09 asks: 'Which atom contains the most neutrons?' followed by four multiple-choice options: A is 54Cr, B is 55Mn, C is 57Fe, and D is 58Ni. Each option has a selection box beside it. Below the question, there is introductory text for subsequent questions 10 and 11.
Question text

09 Which atom contains the most neutrons?

[1 mark]

A 54Cr

B 55Mn

C 57Fe

D 58Ni

Mark scheme

Show the mark scheme Mark scheme table shows question 9 has correct answer C, worth 1 mark (AO1), corresponding to 57Fe.

9 C 1 (AO1) 57Fe

How to answer it

Determining Numbers of Neutrons in Transition Metal Isotopes

📌 What this question tests

This question assesses your fundamental knowledge of atomic structure from Topic 3.1.1 (Atomic Structure):

  • Understanding mass number (A) as the total number of protons plus neutrons.
  • Looking up atomic numbers (proton number, Z) from the Periodic Table for 3d transition elements.
  • Calculating the number of neutrons using the relationship: Number of neutrons = Mass Number (A) − Atomic Number (Z).
Question 09

Multiple Choice: Identifying the Atom with the Most Neutrons

Total: 1 Mark [AO1]

✅ Correct Answer

C: ⁵⁷Fe

Iron-57 contains 31 neutrons, whereas each of the other three atoms contains only 30 neutrons.

Mark Scheme Breakdown:
• 1 mark for selecting option C (AO1 recall & deduction).

💡 Key Knowledge

  • Mass Number (A): Given as the superscript in the symbol (e.g. ⁵⁴Cr has A = 54).
  • Atomic Number (Z): Not shown in the question; must be located on the AQA Data Sheet Periodic Table.
  • Formula: Neutrons = A − Z

📐 Step-by-Step Calculation Breakdown

Using the AQA Periodic Table to find the atomic number (Z) of each element:

Option Isotope Mass Number (A) Atomic Number (Z) Calculation (A − Z) Number of Neutrons
A ⁵⁴Cr 54 24 54 − 24 30
B ⁵⁵Mn 55 25 55 − 25 30
C ⁵⁷Fe 57 26 57 − 26 31 (Highest)
D ⁵⁸Ni 58 28 58 − 28 30

🧠 Exam Technique & Speed Tactics

  • Notice the trap: Examiners deliberately set three distractors that give identical values (30 neutrons). When calculating, if three options give the exact same result, the outlier (31) is almost certainly the right answer.
  • Don't confuse Z and Ar: Transition elements have atomic numbers close to each other (24 to 28), but relative atomic masses listed on the periodic table are decimal numbers (e.g., Fe = 55.8, Ni = 58.7). Always use the integer atomic number (bottom integer in AQA periodic tables).
  • Watch out for Cobalt: Notice that Nickel (Z = 28) skips past Cobalt (Z = 27). Do not just assume consecutive atomic numbers when scanning quickly!

❌ Common Student Errors

  • Selecting D purely because it has the largest mass number: Students under time pressure often pick ⁵⁸Ni assuming the highest mass number means the most neutrons. However, Ni has an atomic number of 28, leaving only 30 neutrons.
  • Misreading the Periodic Table: Reading the atomic number of Iron as 56 (its standard rounded relative atomic mass) rather than 26 (its proton number).
  • Arithmetic slips: Forgetting that Nickel is element 28, not 27 (Cobalt is 27), leading to an incorrect deduction of 58 − 27 = 31.

Topics

Physical Chemistry · 3.1.1 Atomic Structure

Question and mark scheme from the AQA A-Level Chemistry examination, AS Paper 1, June 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.