 Solution

ID: past-exam-of-the-chemistry-course-of-the-year-3-of-the-natural-sciences-course-of-the-university-of-cambridge/2022/paper-1/4/a/solution

An alpha decay decreases mass number by four and atomic number by two; a beta-minus decay keeps the mass number fixed and increases atomic number by one. Therefore

A =_{93}^{239} Np, B =_{94}^{239} Pu, C =_{92}^{235} U .

The beta-minus step converts a neutron to a proton with emission of an electron and an electron antineutrino. It is not capture of an orbital electron, which would change the atomic number in the opposite direction.

 New to topics? Read the docs here!