The gynoecium represents the female reproductive part of the flower and consists of pistil. Each pistil has three parts,

i.e., stigma, style and ovary. Inside the ovarian cavity, the placenta is located.
Arising from the placenta, there are the megasporangia, commonly called ovules. The functional megaspore undergoing the meiotic division develops into the female gametophyte or embryo sac.
In option ' ' thalamus is not a part of gynoecium. Thalamus is the part of flower which form the base on which all the floral whorls rest upon, it is not associated with gynoecium. In option ' ' tapetum is not a part of gynoecium. Tapetum is the inner most nutritive layer of microsporangium and in option ' ' stamen is not a part of gynoecium. Stamen is male reproductive part (androecium) of plant.