The correct option is
B Hybrid sterility
Hybrid zygotes sometimes develop into adults, such as mules (hybrids between female horses and male donkeys), but the adults fail to develop functional gametes and are sterile. This phenomenon is called as hybrid sterility. Thus, option B is correct.
Heterosis, also called hybrid vigour, the increase in such characteristics as size, growth rate, fertility, and yield of a hybrid organism over those of its parents. Plant and animal breeders exploit heterosis by mating two different pure-bred lines that have certain desirable traits. Thus, option A is wrong.
In some cases, no barriers exist to mating between members of different species. In these cases, the zygote formed is called a hybrid zygote. Thus, option C is wrong.
Fertility ability of a hybrid is called as hybrid fertility. Thus, option D is wrong.