The fluid filled cavity present in the tertiary follicle is known as:

The correct answer is Option (2) → Antrum

As a follicle grows, the granulosa cells around the oocyte give out fluid, which collects in a space called the antrum. A follicle with an antrum is a tertiary follicle.

Option (1) Zona pellucida — Incorrect. It is a clear layer around the oocyte itself, not a cavity.

Option (2) Antrum — Correct. The tertiary follicle is marked by a fluid-filled cavity called the antrum. It forms as the secondary follicle grows, and the follicle then changes into the mature Graafian follicle.

Option (3) Theca interna — Incorrect. It is the inner layer of the theca, the cell wall around the follicle.

Option (4) Corpus luteum — Incorrect. It forms from the ruptured Graafian follicle after ovulation and makes progesterone.

NCERT Extract:
Gametogenesis – “… The primary follicles get surrounded by more layers of granulosa cells and a new theca and are called secondary follicles. The secondary follicle soon transforms into a tertiary follicle which is characterised by a fluid filled cavity called antrum. The theca layer is organised into an inner theca interna and an outer theca externa.”