When a nucleus undergoes radioactive \({\beta ^ + }\) decay, the change in the number of particles in the universe is

A.     0.

B.     1.

C.     2.

D.     3.

C

A number of candidates neglected the neutrino accompanying \({\beta ^ + }\) decay. Some candidates may have over-complicated the question by considering subsequent reactions (such as pair annihilation), following the \({\beta ^ + }\) decay.