NEETprep Answer:

$\mathrm{Megaspore} \mathrm{mothercell} \left(2\mathrm{n}\right)\stackrel{\mathrm{Melosis}}{\to }\mathrm{Megaspores}\stackrel{\mathrm{Mllosis}}{\to }\mathrm{Embryo} \mathrm{sac}\left(\mathrm{n}\right)$

The diploid Megaspore Mother Cell (MMC) undergo meiosis and forms linear tetrad of four haploid megaspores. Three mitotic divisions, inside the functional (one) megaspore, form the embryo sac(eight haploid nuclei), while the other three megaspores degenerate. The embryo sac is a seven-celled and eight nucleated structure, Three micropylar, Three chalazal and one central. The three micropylar cells are collectively known as egg-apparatus, which, consists of two synergids and one egg cell.
While three chalazal cell form antipodal cell. The central cell is in the form of two nucleated cell till the fertilisation occurs and called as polar nuclei.