Which are the outermost and the innermost wall layers, respectively,…

The correct answer is Option (3) → Epidermis and tapetum

In a transverse section, a microsporangium is surrounded by four wall layers. Going from outside to inside they are the epidermis, endothecium, middle layers and the tapetum.

Option (1) Endothecium and tapetum — Incorrect. The endothecium is the second layer, just inside the epidermis, so it is not the outermost layer.

Option (2) Epidermis and middle layers — Incorrect. The epidermis is the outermost layer, but the middle layers lie between the endothecium and the tapetum, not on the inside.

Option (3) Epidermis and tapetum — Correct. The epidermis is the outermost and the tapetum the innermost wall layer. The tapetum nourishes the developing pollen grains.

Option (4) Endothecium and middle layers — Incorrect. Neither of these is at the edge of the wall. The endothecium is the second layer and the middle layers come third.

NCERT Extract:
Stamen, Microsporangium and Pollen Grain – “… Structure of microsporangium: In a transverse section, a typical microsporangium appears near circular in outline. It is generally surrounded by four wall layers (Figure 1.3b)– the epidermis, endothecium, middle layers and the tapetum. The outer three wall layers perform the function of protection and help in dehiscence of anther to release the pollen. The innermost wall layer is the tapetum. It nourishes the developing pollen grains.”

Figure 1.3 (b) Enlarged view of one microsporangium showing wall layers