Worked example
An atom has atomic number 8. How many protons does it have?
Answer & why
Answer: 8
Atomic number equals proton count, so there are 8 protons.
Grade 10 · Science
Count protons, neutrons and electrons
Use atomic number, mass number and charge to count particles in a simple atomic model.
6 authored questions + worked example
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All questions
All 6 authored questions for this skill.
Question 1
A neutral atom has 10 protons. How many electrons does it have?
- 6
- 8
- 11
- 10
A hint
Atomic number counts protons; mass number is protons plus neutrons.
Answer & why
Answer: 10
Neutrality requires 10 negative electrons to balance 10 positive protons.
Question 2
A sodium ion has 11 protons and a 1+ charge. How many electrons does it have?
- 10
- 8
- 6
- 11
A hint
Atomic number counts protons; mass number is protons plus neutrons.
Answer & why
Answer: 10
A 1+ ion has one fewer electron than proton: 11 − 1 = 10.
Question 3
An oxide ion has 8 protons and a 2− charge. How many electrons does it have?
- 6
- 8
- 10
- 11
A hint
Atomic number counts protons; mass number is protons plus neutrons.
Answer & why
Answer: 10
A 2− ion has two extra electrons: 8 + 2 = 10.
Question 4
A nucleus has atomic number 6 and mass number 18. How many neutrons does it have?
- 8
- 6
- 10
- 12
A hint
Atomic number counts protons; mass number is protons plus neutrons.
Answer & why
Answer: 12
Neutrons = mass number − atomic number = 18 − 6 = 12.
Question 5
An atom has atomic number 8. How many protons does it have?
- 10
- 6
- 8
- 11
A hint
Atomic number counts protons; mass number is protons plus neutrons.
Answer & why
Answer: 8
Atomic number equals proton count, so there are 8 protons.
Question 6
A nucleus has 6 protons and mass number 12. How many neutrons does it have?
- 8
- 11
- 6
- 10
A hint
Atomic number counts protons; mass number is protons plus neutrons.
Answer & why
Answer: 6
Neutrons = 12 − 6 = 6.