The most appropriate model of the radioactive decay of a group of atoms among the options provided is popping a bag of popcorn.
This is because, similar to radioactive decay, the process of popcorn popping is random and occurs independently for each kernel, much like how individual atoms decay at unpredictable times. Once a kernel pops (or an atom decays), it cannot "unpop," which aligns with the irreversible nature of radioactive decay.