**Core Concept**
Normal saline is a type of isotonic solution, which means it has the same osmotic pressure as human blood. It is typically composed of 0.9% w/v sodium chloride (NaCl), which dissociates into sodium ions (Na+) and chloride ions (Cl-) in water.

**Why the Correct Answer is Right**
The Na+ concentration in normal saline is calculated based on the dissociation of NaCl in water. Since 0.9% w/v of NaCl is dissolved in 1000 mL of water, and the molecular weight of NaCl is approximately 58.44 g/mol, we can calculate the number of moles of NaCl and subsequently the number of moles of Na+ ions. This results in a concentration of approximately 154 mEq/L of Na+.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is likely too low, as normal saline is designed to be isotonic with human blood, which typically has a Na+ concentration of around 135-145 mEq/L.

**Option B:** This option is likely too high, as normal saline is not hyperosmolar and would not be suitable for intravenous administration at such high concentrations.

**Option C:** This option is likely incorrect, as normal saline does not contain potassium ions (K+), but rather sodium ions (Na+).

**Clinical Pearl / High-Yield Fact**
Normal saline is often used as a maintenance IV fluid in patients, but it can also be used to treat various conditions such as severe dehydration, hyponatremia, and certain types of shock.

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