Which statement most accurately summarizes the primary biological roles of chloride, magnesium, and sulfur?

• A. Chloride functions chiefly as an extracellular electrolyte and component of stomach acid; magnesium is a widespread enzyme cofactor and electrolyte needed for nerve, muscle, and heart function; sulfur is part of certain amino acids and some B vitamins that stabilize protein structure.
• B. Chloride is mainly stored intracellularly for energy production while magnesium forms thyroid hormones and sulfur is the principal ion controlling blood pH.
• C. Magnesium is only important during exercise for ATP breakdown, chloride acts only as a dietary preservative, and sulfur is required exclusively for vitamin C synthesis.
• D. All three minerals primarily function as energy substrates for the Krebs cycle, with sulfur acting as the rate-limiting nutrient and magnesium and chloride as coenzymes for ATP synthesis.

Answer: (A)