On what day does fsh reach its maximum concentration? what is happening with regard to the ovary at this point and what is happening with regard to the menstrual cycle?

On the 12th day the Follicle Stimulating Hormone reach its peak concentration.

 The Follicle stimulating hormone stimulates the growth of the egg-bearing follicles in the ovaries. The levels of Follicle stimulating hormone vary during the menstrual cycle and are best measured at its peak or baseline level. FSH levels level vary during the menstrual cycle, reaching their peak prior to ovulation. It is best to measure FSH on day three of the period via a blood sample which is called the baseline level. It provides the most accurate predictions of ovarian reserve.