Beta decay can happen in two ways as by emitting
an electron or by emitting a positron.
Here, an electron was emitted. In electron
emitting beta decay, a neutron of element converts into a proton by emitting
an electron.
So the daughter element should have same number of
mass number as parent element but there is difference between atomic numbers.
Daughter element will have higher atomic number by 1 than parent element due to
the conversion of a neutron.
Since parent atom is Mo (atomic number / proton
number = 42), after a beta decay, the daughter nucleus
should be the element Tc (atomic number = 43).
