Osmosis causes water to move across cell membranes from areas with less solute to areas with more solute.

True: Sodium is the primary extracellular cation, while chloride is the major extracellular anion, maintaining osmotic balance outside the cell. Active transport by the sodium-potassium pump ensures these ions remain at low concentrations within the cytoplasm. This distribution is critical for cellular hydration and electrical signaling.

A. It decreased the pH of the solution as it increased the amount of bicarbonate: While bicarbonate is part of the buffering system, the immediate reduction in pH is driven by the liberation of hydrogen ions. Bicarbonate itself acts as a conjugate base. The acidification is a result of the formation of carbonic acid.

B. There was no change: Exhaled breath contains a significant partial pressure of carbon dioxide, which is chemically active in aqueous solutions. The interaction between carbon dioxide and water inevitably produces weak acid. This chemical reaction alters the pH and triggers a color change.

C. It decreased the pH of the solution as it increases CO2 in the solution: Dissolved carbon dioxide reacts with water to form carbonic acid, which dissociates into hydrogen and bicarbonate ions. The increased concentration of free protons raises the acidity of the solution. This lower pH is detected by the indicator.

D. It increased the pH of the solution as it increases CO2 in the solution: Carbon dioxide is an acid anhydride and cannot increase the alkalinity of a solution. An increase in carbon dioxide concentration shifts the chemical equilibrium toward the production of more acidic products. This results in a lower pH value.

E. It increased the pH of the solution as it increased the amount of bicarbonate: Higher bicarbonate levels generally contribute to alkalinity or buffering capacity. However, the process of exhaling into the solution primarily introduces carbon dioxide, which acts to acidify the environment. It does not lead to an increase in pH.