**Core Concept**
Serum osmolality is a measure of the concentration of osmotically active particles in the blood, primarily sodium, glucose, and urea. It is an important indicator of fluid balance and electrolyte status in the body.

**Why the Correct Answer is Right**
The normal range of serum osmolality is between 285 and 295 mOsm/L. This range is maintained by the body's ability to regulate the concentration of solutes in the blood through the actions of the kidneys and the hypothalamic-pituitary-adrenal axis. The kidneys regulate serum osmolality by adjusting the amount of water reabsorbed from the glomerular filtrate back into the bloodstream, while the hypothalamic-pituitary-adrenal axis regulates the secretion of antidiuretic hormone (ADH), which helps to concentrate or dilute the urine to maintain serum osmolality within the normal range.

**Why Each Wrong Option is Incorrect**
**Option A:** This value is too low and would indicate hyponatremia, a condition characterized by an abnormally low concentration of sodium in the blood.
**Option B:** This value is too high and would indicate hypernatremia, a condition characterized by an abnormally high concentration of sodium in the blood.
**Option C:** This value is outside the normal range and would indicate a disorder of fluid balance, such as diabetes insipidus, which is characterized by an inability to regulate serum osmolality.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that serum osmolality is a critical parameter in the assessment of patients with altered mental status, seizures, or coma, as these conditions can be caused by disturbances in serum osmolality.

**Correct Answer: C. 285-295 mOsm/L**