A mass of parenchymatous tissue forming the bulk of ovule is

The correct option is B Nucellus

Obturator is a structure of ovule that is associated with directing the growth of pollen tube towards the micropyle. It may originate either from the placenta or funiculus or even both.

Female gametophyte is the embryo sac. It is a 7-celled structure consisting of egg apparatus (comprising of egg cell and two synergids), a large central cell and three antipodal cells.

Nucellus is the central part of ovule in which embryo sac is present. It is a mass of parenchymatous cells and forms the major part of the ovule.

Endosperm is the nutritive structure formed from triple fusion that provides nutrition to the developing embryo.

Hence, from all the options given in the question, the mass of parenchymatous cells forming bulk of ovule is nucellus.

So, the correct answer is C.