question: What are the only type of elements capable of changing into different elements?
distractor3: adjacent elements
distractor1: noble gases
distractor2: metalloids
correct_answer: radioactive elements
support: Some elements naturally change into different elements. To understand how this happens, first recall what an element is. An element is a unique substance, with a unique number of protons in the nucleus of its atoms. No two elements have the same number of protons. For example, carbon atoms always have six protons. If an atom has a different number of protons, it isn’t carbon. For an element to change into a different element, then, it must change the number of protons in the nucleus of its atoms. This happens only in radioactive elements.