Which of the following pairs represents the two main intracellular ions in animal cells?

• A. Calcium (Ca\(^{2+}\)) and sodium (Na\(^+\))
• B. Potassium (K\(^+\)) and phosphate (PO\(_4^{3-}\))
• C. Sodium (Na\(^+\)) and chloride (Cl\(^-\))
• D. Potassium (K\(^+\)) and magnesium (Mg\(^{2+}\))

Answer: (B)

Verified step by step guidance

1. Understand the concept of intracellular ions: Intracellular ions are ions found within the cytoplasm of cells. They play critical roles in maintaining cellular functions such as osmotic balance, enzyme activity, and electrical signaling.
2. Recognize the two main intracellular ions in animal cells: Potassium (K extsuperscript{+}) is the primary cation (positively charged ion) inside cells, while phosphate (PO extsubscript{4} extsuperscript{3-}) is a major anion (negatively charged ion) involved in energy storage and signaling.
3. Eliminate incorrect options: Calcium (Ca extsuperscript{2+}) and sodium (Na extsuperscript{+}) are primarily extracellular ions, meaning they are found outside the cell. Similarly, sodium (Na extsuperscript{+}) and chloride (Cl extsuperscript{-}) are also extracellular ions. Potassium (K extsuperscript{+}) and magnesium (Mg extsuperscript{2+}) are not paired with phosphate, making this option incorrect.
4. Focus on the correct pairing: Potassium (K extsuperscript{+}) is essential for maintaining the cell's resting membrane potential, while phosphate (PO extsubscript{4} extsuperscript{3-}) is a key component of ATP (adenosine triphosphate), the energy currency of the cell.
5. Conclude that the correct answer is Potassium (K extsuperscript{+}) and phosphate (PO extsubscript{4} extsuperscript{3-}), as these are the two main intracellular ions in animal cells.