β⁻ emission is an
emission of an electron from the parent atom while converting a neutron into a
proton.<span> Hence, the formed daughter nucleus has the same
number of mass but the atomic number is higher by 1 and number of neutrons is
lower by one than the parent atom.</span><span>
After a β⁻<span> emission of ¹⁰⁶Ru, the formed daughter nucleus
should have 106 as mass number but (44 + 1) = 45 </span>as the atomic number. </span><span>
<span>Hence the daughter nucleus is </span>Rh<span> (</span>Rhodium<span>) which has </span>45<span> protons
(atomic number).</span></span>
