Some students think only large nuclei can be radioactive
Students are typically familiar with unstable heavy elements such as uranium and plutonium from popular culture, but when presented with a question about carbon-14, they assumed it was a trick question.
Resources to Address This
Use this group activity to explain why some nuclei are stable and others are not. The carbon isotopes used in the question may prompt students to examine their thinking that only heavy nuclei are unstable.
With thanks to the teaching community for submitting this misconception about radioactivity.