To solve this problem, we need to identify which pair of hormones are not antagonistic to each other. Let's analyze each option:$\newline \bullet$Option 1: Parathormone – Calcitonin$\newline$ - Parathormone (PTH) increases blood calcium levels by stimulating osteoclasts, increasing intestinal absorption of calcium, and reducing calcium excretion by the kidneys.$\newline$ - Calcitonin decreases blood calcium levels by inhibiting osteoclast activity and increasing calcium excretion by the kidneys.$\newline$ - Therefore, Parathormone and Calcitonin are antagonistic.$\newline \bullet$Option 2: Insulin – Glucagon$\newline$ - Insulin decreases blood glucose levels by promoting glucose uptake by cells and stimulating glycogen synthesis.$\newline$ - Glucagon increases blood glucose levels by stimulating glycogen breakdown and gluconeogenesis.$\newline$ - Therefore, Insulin and Glucagon are antagonistic.$\newline \bullet$Option 3: Aldosterone – Atrial Natriuretic Factor (ANF)$\newline$ - Aldosterone increases sodium reabsorption in the kidneys, leading to increased blood volume and blood pressure.$\newline$ - Atrial Natriuretic Factor decreases sodium reabsorption, leading to decreased blood volume and blood pressure.$\newline$ - Therefore, Aldosterone and ANF are antagonistic.$\newline \bullet$Option 4: Relaxin – Inhibin$\newline$ - Relaxin is involved in the relaxation of the uterine muscles and the widening of the pelvis during childbirth.$\newline$ - Inhibin inhibits the secretion of follicle-stimulating hormone (FSH) from the anterior pituitary.$\newline$ - Relaxin and Inhibin do not have opposing effects on the same physiological process.$\newline$Therefore, the pair of hormones that are not antagonistic to each other is Relaxin and Inhibin.$\newline$This corresponds to Option 4.