Which of the following ion is most abundant within cell fluid? — s Block Elements Chemistry Question

💡 Solution & Explanation

# Ion Abundance in Cell Fluid **The most abundant ion inside cells is $K^+$ (potassium ion).** ## Step-by-Step Reasoning: 1. **Intracellular vs. Extracellular Distribution** - Inside cells (intracellular fluid): $K^+$ dominates at ~140 mM - Outside cells (extracellular fluid): $Na^+$ dominates at ~145 mM 2. **Na⁺/K⁺-ATPase Pump** - The cell membrane actively pumps 3 $Na^+$ out and 2 $K^+$ in - This maintains high intracellular $[K^+]$ and low intracellular $[Na^+]$ 3. **Other Ions (why they're not most abundant)** - $Na^+$: Low inside cells (~12 mM) - $Ca^{2+}$: Very low (~0.0001 mM) - $Cl^-$: Moderate (~4-5 mM inside) - $Mg^{2+}$: Low (~2 mM) 4. **Physiological Importance** - High $K^+$ maintains cell volume, membrane potential, and protein synthesis - Critical for nerve/muscle function **Answer: $K^+$ (Potassium ion) is the most abundant cation in cell fluid.**