Q. On average what is the life duration of the red blood cells? Where are they destroyed? What is the destination of the heme groups after the destruction of hemoglobin molecules?

The spleen is the main organ where old red blood cells are destroyed, On average red blood cells live around 120 days.

During the red blood cell destruction the heme groups turn into bilirubin and excreted in the bowels as part of the bile and later this substance is then captured by the liver.