• 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

• Mass Spectrometry (MS): An analytical technique that measures the mass-to-charge ratio ($m/z$) of gas-phase ions:
• Ionization: Molecules are ionized using techniques such as Electrospray Ionization (ESI), Matrix-Assisted Laser Desorption/Ionization (MALDI), or Electron Ionization (EI).
• Mass Analyzer: Deflects and resolves ions in electromagnetic fields based on their specific $m/z$ ratio.
• Detector: Quantifies the abundance of ions of each $m/z$, generating a characteristic mass spectrum.

Correct option: (4) Mass spectrometry

• Phase I Xenobiotic Metabolism: Catalyzed by the microsomal Cytochrome P450 monooxygenase system in the smooth endoplasmic reticulum:

• Reducing Equivalents: The required electrons/reducing power are supplied by NADPH, which transfers electrons to cytochrome P450 via the flavoprotein NADPH-cytochrome P450 reductase (containing FAD and FMN).
• Source of NADPH: Mainly generated via the pentose phosphate pathway (HMP shunt).

Correct option: (1) NADPH