The fission reaction of ${}^{235}_{92}\mathrm{U}$ with thermal neutron is represented below.${}^{99}_{41}\mathrm{Nb}$ and ${}^{133}_{51}\mathrm{Sb}$ are the primary fission fragment pair, which undergo series of radioactive decay to form stable nuclei $\mathrm{X_3}$ and $\mathrm{Y_4}$ (chain enders). The $\mathrm{X_3}$ and $\mathrm{Y_4}$, respectively are:
(a)${}^{99}_{44}\mathrm{Ru}$ and ${}^{133}_{55}\mathrm{Cs}$
(b)${}^{96}_{41}\mathrm{Nb}$ and ${}^{130}_{51}\mathrm{Sb}$
(c)${}^{93}_{38}\mathrm{Sr}$ and ${}^{127}_{35}\mathrm{Ag}$
(d)${}^{87}_{35}\mathrm{Br}$ and ${}^{124}_{43}\mathrm{Tc}$