A 5-week-old boy is brought to the emergency department because of vomiting for 9 days. The vomiting occurs within 20 minutes of nearly every feeding, is forceful, and has never been bile-stained; he appears hungry and feeds eagerly immediately afterward. He was born at term after an uncomplicated pregnancy and had been gaining weight normally until the vomiting began. He now weighs 180 g less than his birth weight. Temperature is 36.8°C (98.2°F), pulse is 168/min, respirations are 44/min, and blood pressure is 74/44 mm Hg. Examination shows a depressed anterior fontanelle, dry mucous membranes, and peristaltic waves crossing the upper abdomen; a firm, mobile, olive-shaped mass is palpable in the right upper quadrant. Serum studies are most likely to show which of the following?