An isotonic solution contains equal solute concentration on both sides.

Choice A reason: This is incorrect because low HCO3- and high PaCO2 are signs of metabolic acidosis, not alkalosis. Metabolic acidosis is a condition where the blood pH is lower than the normal range of 7.35 to 7.45, due to an excess of acids or a loss of bases in the body.

Choice B reason: This is incorrect because low PaCO2 and low HCO3- are signs of respiratory acidosis, not alkalosis. Respiratory acidosis is a condition where the blood pH is lower than the normal range of 7.35 to 7.45, due to impaired gas exchange or hypoventilation, which causes carbon dioxide to accumulate in the blood.

Choice C reason: This is correct because low PaCO2 and high HCO3- are signs of alkalosis. Alkalosis is a condition where the blood pH is higher than the normal range of 7.35 to 7.45, due to a loss of acids or an excess of bases in the body. There are two types of alkalosis: respiratory and metabolic. Respiratory alkalosis is caused by hyperventilation, which lowers the PaCO2 in the blood. Metabolic alkalosis is caused by vomiting, diuretics, or excessive intake of antacids, which raises the HCO3- in the blood.

Choice D reason: This is incorrect because high PaCO2 and high HCO3- are signs of compensation, not alkalosis. Compensation is a process where the body tries to restore the normal pH by adjusting the levels of PaCO2 and HCO3- in the opposite direction of the primary disorder. For example, if the patient has metabolic alkalosis, the respiratory system will try to compensate by retaining carbon dioxide and lowering the PaCO2. If the patient has respiratory alkalosis, the renal system will try to compensate by excreting bicarbonate and lowering the HCO3-.

Choice A reason: Narrow, peaked T waves are a sign of hyperkalemia, which is a high level of potassium in the blood. Potassium is an electrolyte that affects the electrical activity of the heart. Hyperkalemia can cause the T waves, which represent the repolarization of the ventricles, to become narrow and peaked, indicating a rapid and excessive repolarization.

Choice B reason: ST elevation is a sign of myocardial infarction, which is a heart attack. It indicates that the myocardium, or the heart muscle, is damaged and deprived of oxygen. ST elevation is not related to the potassium level, but rather to the coronary artery blood flow.

Choice C reason: Peaked P waves are a sign of atrial hypertrophy, which is an enlargement of the atria, the upper chambers of the heart. It indicates that the atria are under increased pressure or workload. Peaked P waves are not related to the potassium level, but rather to the atrial function.

Choice D reason: Prominent U waves are a sign of hypokalemia, which is a low level of potassium in the blood. Potassium is an electrolyte that affects the electrical activity of the heart. Hypokalemia can cause the U waves, which represent the repolarization of the Purkinje fibers, to become prominent and visible, indicating a delayed and prolonged repolarization.