Answer
a. Atomic number of resulting nucleus, high to low: B, C, A.
b. Number of neutrons in resulting nucleus, high to low: C, A, B.
Work Step by Step
a. The atomic number decreases by 2 for alpha emission, because alpha particles carry a charge of +2e.
The atomic number increases by 1 for beta emission, because beta particles carry a charge of -1e.
The resulting atomic numbers, in the order B, C, A, are 92, 91, 90.
These are calculated from data shown in the periodic table of the elements, page 216.
b. The number of neutrons is the atomic mass number minus the atomic number.
The resulting numbers of neutrons, in the order C, A, B, are 149, 146, 145.
These are calculated from data shown in the periodic table of the elements, page 216.