Final answer:
Testosterone is the hormone primarily responsible for muscle growth and the growth of body and facial hair in adolescent males.
Step-by-step explanation:
The hormone primarily responsible for the muscle growth and growth of body and facial hair in adolescent males is testosterone. During puberty, the hypothalamus stimulates the pituitary gland to secrete luteinizing hormone (LH), which then stimulates the testes to produce testosterone. Testosterone is responsible for the development of secondary sexual characteristics in males, such as the deepening of the voice, the growth of facial, axillary, and pubic hair, and an increase in muscle bulk.