A gas is collected from a radioactive material; upon inspection, the gas is identified as helium. the presence of the helium indicates the radioactive sample is most likely decaying by

The presence of helium gas indicates the radioactive sample is most likely decaying by α-decay, or alpha decay. α-decay is the type of radioactive decay in which an atomic nucleus emits α particles. α particles are Helium nuclei. So the correct answer would be α-decay.