The normal RBC count in an adult male is 5.0 million (option 2). RBCs, or red blood cells, are responsible for carrying oxygen throughout the body. A normal RBC count is essential for proper functioning and oxygenation of tissues.

Option 1 (5.5 million) is higher than the normal range. This elevated count, called erythrocytosis, may be seen in conditions such as dehydration, high-altitude living, or certain medical disorders.

Option 3 (4.5 million) is lower than the normal range. This reduced count, known as anemia, may be caused by factors like iron deficiency, vitamin deficiencies, bleeding, or chronic diseases.

Option 4 (4.0 million) is also lower than the normal range and indicates a more severe form of anemia.

Therefore, the correct answer is 2 (5.0 million) as it falls within the normal range for an adult male.