The principal anions in the ICF are:
(a) Phosphate and proteins (Pr⁻)
(b) Phosphate and bicarbonate
(c) Sodium and chloride
(d) Sodium and potassium

Verified step by step guidance

1. Step 1: Understand the terms ICF and anions. ICF stands for intracellular fluid, which is the fluid inside the cells. Anions are negatively charged ions present in this fluid.
2. Step 2: Recall the common ions found inside cells. The principal cations (positively charged ions) inside cells are potassium (K⁺), while the principal anions (negatively charged ions) include phosphate ions and proteins (Pr⁻).
3. Step 3: Analyze each option in the question: (a) Phosphate and proteins (Pr⁻) are known major intracellular anions; (b) Phosphate and bicarbonate - bicarbonate is more abundant in extracellular fluid; (c) Sodium and chloride - these are mainly extracellular ions; (d) Sodium and potassium - both are cations, not anions.
4. Step 4: Conclude that the principal anions in the intracellular fluid are phosphate and proteins (Pr⁻), which corresponds to option (a).
5. Step 5: Remember that the balance of ions inside and outside the cell is crucial for cell function, and the presence of phosphate and proteins as principal anions in the ICF helps maintain this balance.

Key Concepts

Intracellular Fluid (ICF) Composition

The intracellular fluid is the fluid within cells, containing a unique mix of ions and molecules essential for cellular function. Understanding its composition helps distinguish it from extracellular fluid, especially in terms of dominant ions and molecules.

Principal Anions in ICF

Anions are negatively charged ions; in the ICF, the main anions include phosphate ions (PO4³⁻) and negatively charged proteins (Pr⁻). These anions help maintain cell charge balance and participate in metabolic processes.

Difference Between Intracellular and Extracellular Ions

Intracellular fluid is rich in potassium and phosphate ions, while extracellular fluid contains more sodium and chloride ions. Recognizing this difference is key to answering questions about ion distribution in body fluids.