Answer is: the missing daughter nucleus is rhodium (Rh).Nuclear reaction: ¹⁰⁶Ru → ¹⁰⁶Rh + e⁻(electron) + ve(electron antineutrino).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 minus decay, neutron is converted to a proton and an electron and an electron antineutrino.
In beta plus decay, a proton is converted to a neutron and positron and an electron neutrino, so mass number does not change.