# Is there a case when an atom of some element (e.g. carbon) does not have its expected number of protons (e.g. 6)?

Page 12 of the Study Guide for Campbell Biology, 11th Edition has the following question:

1. A carbon atom has 6 neutrons. How many protons are present in the nucleus of a carbon atom?

A. 12
B. 8
C. 6

The answer given on page 431 is D. I think the answer should be C since carbon has 6 protons.

What type of additional information might be required?

I understand that elements are defined by their number of protons, but maybe there is some strange edge case like a moment during nuclear fusion? Is there a case when a carbon atom does not have 6 protons?

• The answer may technically be (d), because without any external knowledge of the Periodic Table, there is no way to infer the number of protons from the number of neutrons... Oct 21, 2018 at 21:38
• @orthocresol That's an interesting idea, thanks. Oct 21, 2018 at 21:46
• @orthocresol it still seems to be a poor question because they do include the reference to carbon. If they just said an atom, that would be better.
– Tyberius
Oct 22, 2018 at 1:46
• All isotopes of carbon have 6 protons. That of course is what makes the atoms carbon. The number of neutrons can, and does, vary. Pure and simple the question has a horribly wrong answer.
– MaxW
Oct 22, 2018 at 4:55

1. A carbon atom has 6 neutrons. How many protons are present in the nucleus of a carbon atom?

Obviously this wording would make any astute student say the answer is 6 since carbon by definition has 6 protons. You are correct, elements are defined by their number of protons. Key word being defined, changing the number of protons changes the element.

I believe the key here that your book is getting at is you only know that you have an atom from a carbon sample that has 6 neutrons but nothing else. I think the question is trying to evaluate if you are aware that proton numbers are independent of neutron numbers thus knowing there are 6 neutrons does not help you determine protons, especially given one of the options is: