Which of the following is not correct ?

Question

(a) Nuclei of atoms participated in nuclear reactions

(b) $_{20}Ca^{40}$ and $_{18} Ar ^{40}$ are isotones

(c) I amu of mass defect is approximately equal to $931.5 MeV$

(d) Urainium $(U^{238})$ series is known as $(4n+2)$ series