In a typical angiosperm, the mature embryo sac is :

8 nucleated, 7 celled

The correct answer is Option (1) – 8 nucleated, 7 celled

The most common type of embryo sac in flowering plants is a Monosporic, 8 nucleated and 7 celled.

In the monosporic type of embryo sac development, a single functional megaspore (out of four megaspores produced by meiosis) undergoes further development to form the embryo sac. The development of the monosporic embryo sac involves three stages: the megaspore stage, the 4-nucleate stage, and the 8-nucleate stage.

During the megaspore stage, the single functional megaspore undergoes three rounds of mitotic divisions without cytokinesis, resulting in an 8-nucleate structure called the initial syncytial stage. At this stage, the embryo sac contains a central cell with two polar nuclei and six peripheral nuclei.

Next, the 4-nucleate stage is reached when cellularization occurs, resulting in the formation of a 4-celled structure. The four cells are the egg cell, two synergids, and the central cell with two polar nuclei.

Finally, the 8-nucleate stage is achieved as the two polar nuclei in the central cell fuse to form a secondary nucleus, resulting in a total of eight nuclei within the embryo sac. The 8-nucleate embryo sac consists of the egg cell, two synergids, three antipodal cells at the chalazal end, and the central cell with two polar nuclei.