Final answer:
Excessive vomiting is the most likely cause of alkalosis, as it leads to the loss of hydrogen and chloride ions, resulting in metabolic alkalosis.
Step-by-step explanation:
The most likely cause of alkalosis from the options provided is excessive vomiting. Excessive vomiting can lead to a condition known as metabolic alkalosis, which occurs due to the loss of hydrogen and chloride ions when hydrochloric acid is expelled from the stomach. Other causes of metabolic alkalosis include loss of potassium due to diuretic use or excessive intake of antacids. Aspirin overdose typically leads to respiratory alkalosis initially due to hyperventilation as the body tries to compensate for initial acidosis, but not metabolic alkalosis.