Answer to Question 1
Substances that can donate or give up hydrogen ions (H+) are considered to be acids. In human physiology, two groups of acids are important: volatile and nonvolatile. Volatile acids are those that can be converted to a gaseous form and eliminated by the lungs. Nonvolatile acids include those inorganic acids that are formed during metabolism of carbohydrate, protein, and lipid. The lungs cannot eliminate nonvolatile acids. Carbonic acid is the most important volatile acid because it is produced in the largest amount and provides the major source of H+.
Answer to Question 2
c