A particle was ejected from the nucleus of an atom in a radioactive decay and the active number of the atom increased. The particle was probably:

Explanation

Beta decay is a radioactive decay in which a beta ray is emitted from an atomic nucleus. The two types of beta decay are known as beta minus and beta plus. In beta minus (β−) decay, a neutron is converted to a proton, and the process creates an electron and an electron antineutrino; This causes an increase in atomic number by 1 with atomic mass unchanged while in beta plus (β+) decay, a proton is converted to a neutron and the process creates a positron and an electron neutrino. β+ decay is also known as positron emission. This causes a decrease in atomic number by 1 with atomic mass unchanged. Normally when they don't mention positive or negative beta decay, we always consider negative beta decay, increasing in atomic number by 1.