Erythropoietin hormone which stimulates R.B.C. formation is produced by :

The correct answer is Juxtaglomerular cells of the kidney.

Detailed Explanation:
Erythropoietin (EPO) is a glycoprotein hormone that plays a crucial role in regulating red blood cell (erythrocyte) production (erythropoiesis) in the body. When oxygen levels in the blood decrease (hypoxia), specialized cells detect this change and stimulate the synthesis and release of erythropoietin.
In adults, about 85% to 90% of erythropoietin is synthesized and secreted by the juxtaglomerular cells (or interstitial cells peritubular capillary bed) of the kidneys. The remaining portion is produced by the liver. Once released into the bloodstream, erythropoietin travels to the bone marrow, where it binds to receptors on erythroid progenitor cells, stimulating them to proliferate and differentiate into mature red blood cells.

Let us evaluate the other options:

• Alpha cells of pancreas: These cells produce glucagon, a hormone that raises glucose levels in the blood, and are not involved in erythropoiesis.
• The cells of rostral adenohypophysis: The adenohypophysis (anterior pituitary gland) secretes hormones like growth hormone (GH), thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), and prolactin. It does not produce erythropoietin.
• The cells of bone marrow: While bone marrow is the site of action where red blood cells are formed under the influence of erythropoietin, it does not produce the hormone itself.