The fertilized eggs in human females gets implanted in uterus

The correct option is "after about 7 days of fertilization".

To understand why this is correct, let's break down the sequence of events that occur after fertilization in human reproduction step-by-step:

1. Fertilization:
Fertilization is the union of a sperm cell and an egg cell (ovum) to form a single-celled zygote. This process typically takes place in the fallopian tube (specifically in the ampulla region) shortly after ovulation.

2. Cleavage and Development:
Following fertilization, the zygote begins to divide rapidly by mitosis (cleavage) as it moves down the fallopian tube toward the uterus. It develops from a single cell into a solid ball of cells called a morula (around day 3 to 4), and then into a hollow, fluid-filled ball of cells called a blastocyst (around day 5 to 6).

3. Arrival in the Uterus:
The blastocyst reaches the uterine cavity approximately 5 days after fertilization.

4. Implantation:
Once inside the uterus, the blastocyst hatches from its outer protective coat (zona pellucida) and begins to attach itself to the thickened, nutrient-rich inner lining of the uterus, known as the endometrium. This attachment and embedding process is called implantation. It typically begins around day 6 to 7 after fertilization and is completed by day 10 to 12.

Therefore, the implantation process commences after about 7 days of fertilization, making the first option the correct explanation.