A typical angiosperm embryo sac at maturity is :

The correct option is 8-nucleate and 7-celled.

Step-by-Step Explanation:
An embryo sac represents the female gametophyte in angiosperms. The development and structure of a typical, mature angiosperm embryo sac (also known as the Polygonum type) can be understood through the following breakdown:

1. Nuclear Divisions (Karyokinesis):
The functional megaspore undergoes three sequential mitotic nuclear divisions without immediate cytokinesis (cell wall formation).
- The first mitotic division produces 2 nuclei.
- The second mitotic division produces 4 nuclei.
- The third mitotic division produces 8 nuclei.
Thus, the embryo sac initially contains 8 free nuclei.

2. Cellular Organization (Cytokinesis):
After the 8-nucleate stage, cell walls are laid down, organizing most of the nuclei into distinct cells:
- Egg Apparatus (3 cells at the micropylar end): Consists of one egg cell and two synergids. Each of these three cells contains one nucleus (total 3 nuclei).
- Antipodals (3 cells at the chalazal end): Consists of three cells, each containing one nucleus (total 3 nuclei).
- Central Cell (1 large cell in the center): The remaining two nuclei, called polar nuclei, move to the center and remain within the large single central cell. They do not immediately fuse, so this single cell contains two nuclei (total 2 nuclei).

3. Total Count at Maturity:
Adding up the cells and nuclei:
- Number of cells = 3 (egg apparatus) + 3 (antipodals) + 1 (central cell) = 7 cells.
- Number of nuclei = 3 (in egg apparatus) + 3 (in antipodals) + 2 (in central cell) = 8 nuclei.

Therefore, a typical angiosperm embryo sac at maturity is 8-nucleate and 7-celled.