How many embryo sacs are present in $100$ mature female gametophytes?

The haploid cell which divides by mitosis to form the embryo sac is:

Which of the following is the female gametophyte?

In angiosperms,the following events occur during megasporogenesis and megagametogenesis:
$(i)$ Differentiation of megaspore mother cells
$(ii)$ Meiosis of the megaspore mother cell
$(iii)$ Formation of a linear tetrad
$(iv)$ Mitotic division of the functional megaspore
$(v)$ Degeneration of $3$ megaspores
$(vi)$ Formation of embryo sac
$(vii)$ Fusion of polar nuclei
The correct sequence is:

In the given figure,what do 'a','b',and 'c' represent respectively?

Which of the following is true for a typical mature embryo sac?