Question

Differentiate between primary oocyte and a secondary oocyte.

Answer 1

A female germ cell involved in fertilization is called an oocyte. It's also known as ovum, or egg cell, in other words. It occurs in the ovarian follicle, a specialized unit of the ovary, during the course of oogenesis/folliculogenesis in the cortex. And it is one of the largest cells in the body (approximately $110m$ in diameter).

Complete answer:

Primary oocyte	Secondary oocyte
When the gamete mother cell, oogonia, is arrested in Prophase-I of meiosis, a diploid cell called a primary oocyte is produced.	During puberty, a secondary oocyte is a haploid cell that develops from a primary oocyte and performs the first meiotic division, producing female gamete ova (n).
It is surrounded by secondary follicles	It is surrounded by tertiary follicles.
The chromosome number in the primary oocyte is $46$.	The chromosome number in the secondary oocyte is $23$.

Additional information:
During female gametogenesis, the ovary produces an oocyte. Oogonia is formed when female germ cells create a primordial germ cell (PGC), which then undergoes mitosis. The oogonia become primary oocytes during oogenesis. In a cryo conservation oocyte is stored in the form of genetic material.

Note:
In most anisogamous species, the egg cell, or ovum (plural ova), is the female reproductive cell, or gamete (organisms that reproduce sexually with a larger, "female" gamete and a smaller, "male" one). When the female gamete is unable to move, this word is used (non-motile). When you ovulate, the egg is released from the follicle in a matter of minutes or hours. The egg is only viable for $12 - 24$ hours after it is released, and it must be fertilized by sperm within that time frame.