**Core Concept**
Normal saline is a commonly used intravenous fluid in clinical practice, composed of sodium chloride (NaCl) dissolved in water. The solution has a specific concentration of sodium ions (Na+) that is crucial for maintaining fluid and electrolyte balance in the body.

**Why the Correct Answer is Right**
Normal saline contains 0.9% w/v sodium chloride, which translates to a concentration of 154 mEq/L of sodium ions. This concentration is isotonic to human plasma, meaning it has the same osmotic pressure as blood, and is therefore suitable for intravenous administration. The sodium content in normal saline is essential for maintaining the balance of fluids and electrolytes in the body, particularly in patients who require IV fluids.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because normal saline does not contain a significant amount of potassium ions (K+), which are present in other types of IV fluids like lactated Ringer's solution.

**Option B:** This option is incorrect because normal saline is not hypotonic, meaning it does not have a lower concentration of solutes than human plasma. A hypotonic solution would have a lower concentration of sodium ions than normal saline.

**Option C:** This option is incorrect because normal saline does not contain a significant amount of calcium ions (Ca2+), which are present in other types of IV fluids like calcium gluconate.

**Clinical Pearl / High-Yield Fact**
The sodium content in normal saline is a critical factor in maintaining fluid and electrolyte balance in the body. It is essential to choose the correct type of IV fluid based on the patient's clinical condition to avoid complications like hyponatremia or hypernatremia.

**Correct Answer: C. 154 mEq/L**