Which statement is true of unstable isotopes?

A)Nuclei of light elements are very unstable.B)The nuclei of atoms that are the most unstable have proton to neutron ratios of 1 to 1.C)An unstable atom is an atom that has enough binding energy to hold the nucleus together permanently.D)An unstable isotope is one that undergoes spontaneous nuclear decay and is referred to as a radioisotope.