Answer to Question 1
D
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Carbonic anhydrase, an enzyme, speeds the process of carbon dioxide and water combining to form carbonic acid. The carbonic acid immediately dissociates to form sodium bicarbonate, using a sodium ion from the renal tubule and a free hydrogen ion (an acid). The other options are not correct.
Answer to Question 2
C
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As sodium is actively moved out of the filtrate, it takes chloride ions and water with it. Sodium does not take calcium, magnesium, or potassium ions with it.