Final answer:
The likely mode of decay for Mo-109 is beta emission (β emission), where a proton is converted to a neutron and a beta particle (electron) is emitted.
Step-by-step explanation:
The likely mode of decay for Mo-109 would be beta emission (β emission).Mo-109 has a neutron-to-proton ratio of only 1.05, which is much less than the requirement for stability for an element with an atomic number in this range. Nuclei that have low neutron-to-proton ratios decay by converting a proton to a neutron. In this case, beta emission occurs where a proton is converted to a neutron and a beta particle (electron) is emitted.