The correct option is B Diploid
A protonema is a thread-like chain of cells, that forms the earliest stage (the haploid phase) of the life cycle of moss. When it first grows from the spore, it grows as a protonema, which develops into a leafy gametophore. If a moss protonema is developed from few cells of the moss capsule wall (diploid in nature), then most probably it will be diploid.