Innermost layer of cortex is :-
A. Endodermis
B. Epidermis
C. Exodermis
D. Hypodermis

Hint: The outermost layer of a stem or root in a plant is called cortex. It is below the epidermis but outside the vascular bundles. The cortex constitutes large thin-walled parenchyma cells of the ground tissue system.

Complete answer:
There are various layers of cells in the root. There is a cortical layer that is present on the innermost side and it is termed as the endodermis.
Therefore, the innermost layer of the cortex is the endodermis.
The cells of endodermis are barrel-shaped. They have a closely packed structure and the thickening is called as casparian strips.
(A) Endodermis: The Endodermis is the central, innermost layer of cortex in land plants. It is cylinder in shape and has compact living cells. Its radial walls have hydrophobic substances (Casparian strip) to stop apoplastic flow of water to the inside. So the endodermis acts as a boundary between the cortex and the stele. The endodermis is the innermost part of the cortex. The cells of the endodermis have primary cell walls which are thickened on all four sides.So "A" is the correct answer.
(B) Epidermis: The epidermis is a single layer of cells that covers the leaves, flowers, roots and stems of plants. The epidermis is the outermost cell layer of the primary plant body. The cells of the epidermis are structurally and functionally variable. The epidermis have various functions such as protection against water loss, regulating gas exchange and mainly absorption of water in roots. So "B" is not the correct answer.
(C) Exodermis: The exodermis is a physiological barrier that has a role in root function and protection. The exodermis is a membrane of variable permeability responsible for the radial flow of water, ions, and nutrients. It is the outer layer of a plant's cortex. So "C" is not the correct answer.
(D) Hypodermis: The outermost layer of a portion of the cortex. A layer or layers of cells that lie beneath the epidermis and are different in appearance from adjacent tissues. It forms a layer just under the epidermis in most of the plants. So "D" is not the correct answer.

Hence, the correct answer is option (A).

Note: Endodermis and epidermis are two cell layers found in the stem and root of the plant. The endodermis is found between the cortex and the vascular tissue. The main difference between endodermis and epidermis is that endodermis is an inner cell layer whereas epidermis is the outermost layer of cells.