Which of the following are commonly found as plasma electrolytes in the human body?

• A. Fe^{2+}, Cu^{2+}, Zn^{2+}, Mn^{2+}
• B. C_6H_{12}O_6, CH_3COO^-, NH_4^+, H_2O
• C. Na^+, K^+, Cl^-, HCO_3^-
• D. NO_3^-, SO_4^{2-}, PO_4^{3-}, CO_2

Answer: (C)

Verified step by step guidance

1. Understand that plasma electrolytes are ions dissolved in the blood plasma that help maintain fluid balance, nerve function, and muscle function.
2. Identify that common plasma electrolytes are small, charged species such as sodium (Na^+), potassium (K^+), chloride (Cl^-), and bicarbonate (HCO_3^-), which are essential for physiological processes.
3. Recognize that the ions Fe^{2+}, Cu^{2+}, Zn^{2+}, and Mn^{2+} are trace metals and not typically considered major plasma electrolytes.
4. Note that molecules like C_6H_{12}O_6 (glucose), CH_3COO^- (acetate), NH_4^+ (ammonium), and H_2O (water) are present in the body but are not classified as primary plasma electrolytes.
5. Understand that other ions such as NO_3^-, SO_4^{2-}, PO_4^{3-}, and CO_2 are present in the body but are not the main electrolytes responsible for plasma osmolarity and electrical neutrality.