Only the H+ ions that are free in solution will contribute to the pH of that solution.

Correct Answer: A

Rationale: Step 1: pH is a measure of the concentration of H+ ions in a solution. Step 2: Only free H+ ions can interact with water molecules to affect pH. Step 3: Bound H+ ions in compounds do not directly impact pH. Step 4: Therefore, only free H+ ions contribute to the pH of a solution. Step 5: Thus, the statement that only free H+ ions contribute to pH is TRUE. Other choices are incorrect as they do not provide a logical explanation for the concept.

Correct Answer: A

Rationale: Step 1: Metabolic acidosis results from an increase in acid levels in the body due to a non-respiratory cause. Step 2: If metabolic acidosis is caused by a pulmonary disease, it implies that the respiratory system is already compromised. Step 3: When the respiratory system is affected by a pulmonary disease, its ability to buffer the acid-base imbalance is diminished. Step 4: Therefore, if metabolic acidosis is caused by a pulmonary disease, the respiratory system cannot effectively act as a buffering system. Summary: Choice A is correct because when a pulmonary disease causes metabolic acidosis, the respiratory system's buffering capacity is impaired. Choices B, C, and D are incorrect as they do not explain the relationship between pulmonary disease and metabolic acidosis.

Correct Answer: B

Rationale: The correct answer is B: FALSE. The kidneys are not the first line of defense against changes in acid-base balance; they are the second line of defense. The first line of defense is the buffer systems in the body, which include bicarbonate, phosphate, and proteins. These buffer systems act quickly to prevent drastic changes in pH. The kidneys come into play as a slower but more powerful mechanism for maintaining pH by regulating the excretion or retention of hydrogen ions and bicarbonate ions. Therefore, while the kidneys are crucial in long-term regulation of acid-base balance, they are not the first line of defense.

Correct Answer: B

Rationale: The correct answer is B: FALSE. The respiratory system can partially compensate for metabolic acidosis by increasing ventilation to eliminate excess CO2. However, it cannot completely compensate as it cannot directly regulate bicarbonate levels in the blood. The kidneys play a crucial role in fully compensating for metabolic acidosis by excreting hydrogen ions and reabsorbing bicarbonate. Choice A is incorrect because the respiratory system alone cannot fully compensate for metabolic acidosis. Choices C and D are not applicable as they do not provide any relevant information regarding the statement.

Correct Answer: B

Rationale: The correct answer is B: Serum sodium of 120 mg/dL. In SIADH, there is excessive release of ADH, leading to water retention and dilutional hyponatremia. A serum sodium level of 120 mg/dL indicates severe hyponatremia and requires immediate intervention to prevent neurological complications. Choice A is incorrect because a serum hematocrit of 42% does not directly relate to SIADH. Choice C is incorrect because a urinary output of 280 mL in 8 hours is not a significant concern in SIADH as the condition leads to water retention and concentrated urine. Choice D is incorrect because a reported weight gain of 2.2 pounds could be related to fluid retention but is not as urgent as addressing severe hyponatremia in SIADH.