What mode of radioactive decay is most likely for the na-20 isotope?

Answer is: beta plus decay (75%).

Nuclear reaction: ²⁰Na → ²⁰Ne + e⁺ (positron) + ve (electron neutrino).

Beta decay is radioactive decay in which a beta ray and a neutrino are emitted from an atomic nucleus.

There are two types of beta decay: beta minus and beta plus.

In beta plus decay, a proton is converted to a neutron and positron and an electron neutrino, so mass number does not change.

In beta minus decay, neutron is converted to a proton and an electron and an electron antineutrino.