• Electrolyte Distribution in Body Fluids:
• Intracellular Fluid (ICF): Potassium ($\text{K}^+$) is the predominant intracellular cation, maintaining a normal concentration of approximately $140\text{--}150\text{ mmol/L}$ (or $\text{mEq/L}$).
• Extracellular Fluid (ECF): The $\text{K}^+$ concentration in plasma is much lower, tightly maintained at $3.5\text{--}5.0\text{ mmol/L}$, whereas sodium ($\text{Na}^+$) is the principal extracellular cation ($135\text{--}145\text{ mmol/L}$).
• Maintenance: This steep electrochemical gradient across animal cell membranes is established and sustained by the plasma membrane $\text{Na}^+/\text{K}^+$-ATPase pump.

Correct option: (1) 140 m mol/L