Question

Negatively charged ions are required to balance the net positive charge from metal ions such as K+, Na+, and Ca2+. Which of the following negatively charged ions is the most abundant outside the cell and which ion does most often neutralize (written in parentheses)?

(a) Cl- (Ca₂₊)
(b) PO₄₃- (K+)
(c) PO₄₃- (Ca₂₊)
(d) Cl- (Na+)

Answer 1

Chloride ions (Cl-) are the most abundant negatively charged ions outside of the cell and most often neutralize sodium ions (Na+), making option (d) Cl- (Na+) the correct answer.

Step-by-step explanation:

The student's question deals with the balance of ions across cell membranes, specifically which negatively charged ion is most abundant outside the cell and what positively charged ion it usually neutralizes. Chloride ions (Cl-) are the most abundant negatively charged ions outside of the cell. These ions help to balance the net positive charge from metal ions such as sodium (Na+) and potassium (K+). The sodium-potassium pump actively transports three Na+ ions out of the cell for every two K+ ions it pumps in, thus leaving a net positive charge outside the cell. Because of this, Cl- ions tend to accumulate outside of the cell to balance the sodium ions. Therefore, the most correct answer to this question is (d) Cl- (Na+), indicating that chloride ions most often neutralize sodium ions.