Nuclei of the isotope nitrogen-14 are bombarded with neutrons and as a result nuclei of an isotope of carbon are produced. The nuclear reaction equation for this process may be written as

\[_7^{14}{\rm{N}} + {\rm{neutron}} \to {}_6^A{\rm{C}} + {\rm{proton}}\]

What is the nucleon number A of the isotope of carbon?

A. 12

B. 13

C. 14

D. 15

C

Many candidates opted for B, presumably assuming that a neutron had no mass.