**Core Concept**
Delayed puberty in males refers to a condition where the secondary sexual characteristics do not develop by the age of 14 years. The most common cause of delayed puberty in males is hypogonadism, which can be primary or secondary. Primary hypogonadism involves a problem with the testes, whereas secondary hypogonadism involves a problem with the hypothalamic-pituitary axis.

**Why the Correct Answer is Right**
The most common cause of delayed puberty in males is Klinefelter syndrome, which is a form of primary hypogonadism. Klinefelter syndrome is characterized by the presence of an extra X chromosome (47,XXY) in males. This leads to impaired testicular function, resulting in low levels of testosterone and follicle-stimulating hormone (FSH). The decreased levels of testosterone disrupt the normal process of puberty, leading to delayed development of secondary sexual characteristics.

**Why Each Wrong Option is Incorrect**
* **Option A:** Constitutional delay of growth and puberty is a common cause of delayed puberty in males, but it is not the most common cause. It is a benign condition that often runs in families.
* **Option B:** Turner syndrome is a genetic disorder that affects females, not males. It is characterized by the absence of one X chromosome (45,X) in females.
* **Option C:** Prader-Willi syndrome is a genetic disorder that affects males and females. It is characterized by short stature, obesity, and hypogonadism, but it is not the most common cause of delayed puberty in males.

**Clinical Pearl / High-Yield Fact**
Klinefelter syndrome is the most common sex chromosome disorder in males and is often associated with infertility, learning disabilities, and an increased risk of autoimmune disorders.

**Correct Answer: C. Klinefelter syndrome**