Which statement correctly identifies structures 1 and 2 in the diagram?

A. Structure 1 is an unstable atom that turns into
structure 2, a new atom.

B. Structure 1 is a stable element that breaks down into structure 2, an unstable element.

C. Structure 1 is a radioactive element that loses particles to create structure 2, released energy.

D. Structure 1 is a radioactive atom that decays into
structure 2, half of the original unstable element.