Question

Why is the period between 10 and 17 days of menstrual cycle called fertile period?

Answer 1

The ovulatory phase of the menstrual cycle occurs in the middle of the menstrual cycle i.e it occurs between the 10${}^{th}$ and the 18${}^{th}$ day of the menstrual cycle.
During this period there is an increase in the luteinizing hormone (LH) level which causes the mature follicle to burst and release the egg (usually around day 14). This is called ovulation.
The best days for conception generally is 11${}^{th}$ to 17${}^{th}$ days leading up to and immediately following ovulation. It is also called the fertile period.