The correct option is B 3n
In the question, the egg is diploid but the ploidy of the male gamete has not been given. Instead, we have been provided with the ploidy of the parent plant which is diploid. Hence, male gamete of such a plant will be haploid. Thus, the embryo resulting from the fusion of the given diploid egg cell and the haploid male gamete will result in the formation of a triploid embryo.