Question

Most diffusible ion across the cell membrane is?

• A. Na+
• B. K+
• C. Cl-
• D. None

Hint:

Compare the cations with the chief diffusible anion of the body.

Answer 1

The Correct Option is C

Step 1: The core of the plasma membrane is a hydrophobic lipid bilayer. It strongly resists the passage of charged, water-soluble particles such as ions, glucose and urea, while letting fat-soluble molecules like oxygen, carbon dioxide and alcohol cross easily.

Step 2: The ease with which an ion crosses is described by its permeability coefficient. Among the listed ions, chloride (Cl-) has the highest membrane permeability and crosses the bilayer most readily compared with sodium and potassium.

Step 3: Sodium (option a) is largely kept out and pumped back by active transport, and potassium (option b), though more permeable than sodium, is still less diffusible than chloride. Therefore chloride is the most diffusible ion of the group.

Step 4: Because Cl- moves most freely, option c is correct.