Question

Nearly 90% of positively charged ions present in the extracellular fluid are

• A. Potassium ion
• B. Sodium ion
• C. Calcium ion
• D. Sulphate ion

Hint:

Electrolyte Partitioning:
Major Extracellular Cation ($> 90\%$) = Sodium ($\text{Na}^+$).
Major Intracellular Cation = Potassium ($\text{K}^+$).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Body fluid compartment electrolyte distribution: sodium ($ ext{Na}^+$) is the predominant extracellular cation, and potassium ($ ext{K}^+$) is the predominant intracellular cation.
Key Formula or Approach:
\[ [\text{Na}^+]_{\text{ECF}} \approx 140 - 145\text{ mEq/L} \quad \gg \quad [\text{K}^+]_{\text{ECF}} \approx 4 - 5\text{ mEq/L}, \quad [\text{Ca}^{2+}]_{\text{ECF}} \approx 2.5\text{ mEq/L} \]

Step 2: Detailed Explanation:
Electrolyte partitioning in animal physiology:
- In the Extracellular Fluid (ECF) (plasma and interstitial fluid):
- The total cation concentration is approximately $150\text{ mEq/L}$, of which Sodium ions ($\text{Na}^+$) account for $142\text{ mEq/L$ (over $90\%$ of all ECF cations)}.
- Conversely, Potassium ($ ext{K}^+$) is the primary intracellular cation ($[\text{K}^+]_{\text{ICF}} \approx 140 - 150\text{ mEq/L}$).

Step 3: Final Answer:
Therefore, nearly 90% of positively charged ECF ions are Sodium ions, matching option (B).