MCQs — Atomic Structure

Practice questions for Chemistry.

← Back to Atomic Structure

Question 41

Isotopes of an element that are unstable and emit radiation as they decay are called:

A. Cations

B. Radioisotopes

C. Anions

D. Molecules

Question 42

Why do radioisotopes emit radiation while most other isotopes do not?

A. Radioisotopes have unstable nuclei that release energy and particles as they decay toward a more stable form

B. All isotopes emit radiation constantly

C. Radioisotopes contain no protons

D. Radioisotopes have no neutrons at all

Question 43

The particle responsible for most of an atom's mass, together with the proton, is the:

A. Electron

B. Photon

C. Neutron

D. Positron

Question 44

An unknown particle has no charge and is found inside the nucleus of an atom. This particle is most likely a:

A. Proton

B. Electron

C. Ion

D. Neutron

Question 45

An unknown particle is deflected toward the positively charged plate when passed through an electric field, and has a very small mass compared to protons and neutrons. This particle is most likely a(n):

A. Proton

B. Neutron

C. Electron

D. Alpha particle

Question 46

The number of protons present in the nucleus of an atom is called its:

A. Atomic number

B. Mass number

C. Isotope number

D. Valency

Question 47

The atomic number of an element determines its:

A. Colour only

B. Identity (which element it is)

C. Physical state only

D. Melting point only

Question 48

Why is the atomic number considered unique to each element?

A. All elements share the same atomic number

B. Atomic number depends only on the number of neutrons

C. Atomic number changes randomly for the same element

D. No two different elements have the same number of protons in their atoms

Question 49

In a neutral atom, the atomic number is also equal to the number of:

A. Neutrons only

B. Electrons

C. Protons and neutrons combined

D. Isotopes

Question 50

An atom has 11 protons in its nucleus. Based on this atomic number, this atom must be an atom of:

A. Neon

B. Magnesium

C. Aluminium

D. Sodium

Question 51

The total number of protons and neutrons in the nucleus of an atom is called its:

A. Atomic number

B. Mass number (nucleon number)

C. Relative atomic mass

D. Isotope number

Question 52

Mass number is represented by which relationship?

A. Mass number = number of protons - number of neutrons

B. Mass number = number of protons only

C. Mass number = number of neutrons only

D. Mass number = number of protons + number of neutrons

Question 53

How can the number of neutrons in an atom be calculated if the atomic number and mass number are known?

A. Number of neutrons = mass number - atomic number

B. Number of neutrons = mass number + atomic number

C. Number of neutrons = atomic number only

D. Number of neutrons cannot be calculated this way

Question 54

An atom has an atomic number of 6 and a mass number of 12. How many neutrons does it contain?

A. 12

B. 18

C. 6

D. 0

Question 55

An atom has an atomic number of 17 and a mass number of 35. How many neutrons does it contain?

A. 18

B. 17

C. 35

D. 52

Question 56

An atom contains 8 protons and 8 neutrons. What is its mass number?

A. 8

B. 24

C. 0

D. 16

Question 57

An atom contains 20 protons and 20 electrons, with a mass number of 40. How many neutrons does this atom contain?

A. 40

B. 0

C. 20

D. 60

Question 58

In the symbol for an atom written as (mass number on top, atomic number on bottom) next to the element symbol, the bottom number represents the:

A. Mass number

B. Atomic number (number of protons)

C. Number of neutrons only

D. Number of electrons lost

Question 59

Two atoms have the same atomic number but different mass numbers. What does this tell us about them?

A. They must be atoms of two completely different elements

B. They must have different numbers of protons

C. They must be ions, not atoms

D. They are isotopes of the same element, with different numbers of neutrons

Question 60

An atom has 15 protons and a mass number of 31. How many electrons does this neutral atom have?

A. 31

B. 15

C. 16

D. 46

🎯 How to get the most out of these questions

Attempt each question before revealing the answer.
Read the explanation even when you answered correctly — it reinforces the concept.
Note down any question you got wrong and revisit it the next day.
Use the pagination below the list to work through every page — do not stop at page 1.

📌 MCQs — FAQs

Are answers included for every question in this section?

Yes — each published question includes an answer. Explanations are shown where they have been added.

Can I print these questions?

Yes — use your browser's print option (Ctrl+P / Cmd+P) to print or save the page as PDF.

How often are questions updated?

New questions are added regularly. If a paper pattern changes, existing questions are reviewed and updated.