The uterine layer responsible for the menstrual bleeding is:

The correct answer is Option (2) → Endometrium

The wall of the uterus has three layers: the outer thin perimetrium, the middle thick myometrium and the inner glandular endometrium that lines the uterine cavity. The endometrium changes in a cycle during the menstrual cycle. When the ovum is not fertilised, its lining breaks down, and this causes menstrual bleeding.

(1) Myometrium — Incorrect. It is the layer of smooth muscle. It contracts strongly during delivery of the baby.

(2) Endometrium — Correct. Its lining and blood vessels break down to give the menstrual flow.

(3) Perimetrium — Incorrect. It is the thin outer membrane of the uterus. It plays no part in menstruation.

(4) Zona pellucida — Incorrect. It is not a layer of the uterus. It is the layer that surrounds the ovum.

NCERT Extract:
The Female Reproductive System – “… The wall of the uterus has three layers of tissue. The external thin membranous perimetrium, middle thick layer of smooth muscle, myometrium and inner glandular layer called endometrium that lines the uterine cavity. The endometrium undergoes cyclical changes during menstrual cycle while the myometrium exhibits strong contraction during delivery of the baby.”
Menstrual Cycle – “… The menstrual flow results due to breakdown of endometrial lining of the uterus and its blood vessels which forms liquid that comes out through vagina.”