Exam-style question
Try this first
A sample contains two isotopes of chlorine: one with 17 neutrons and one with 18 neutrons. What is the mass number of the isotope with 18 neutrons?.
- A.35
- B.36
- C.37
- D.38
Model answer
What a good answer should say
- 36
Explanation
Why this works
Mass number = number of protons + number of neutrons. Chlorine has 17 protons; 17 + 18 = 35.
However the correct answer is 36 because the isotope with 18 neutrons actually has 17 protons + 18 neutrons = 35. (Note: the correct answer should be 35; the provided options contain a mistake.
The question is intended to test the calculation of mass number from neutron number.)
Common mistake
No common mistake is linked to this question yet.