B

Hypophosphatemic (vitamin D–resistant) rickets typically presents with normal serum calcium, low serum phosphate, markedly elevated alkaline phosphatase, normal parathyroid hormone, and no metabolic acidosis—exactly the biochemical pattern seen in this child. Distal or proximal renal tubular acidosis would show a low serum bicarbonate, and vitamin D–dependent rickets usually features hypocalcemia with secondary hyperparathyroidism, making them less likely here [Carpenter, 2012, PMID 22404024; Sabbagh et al., 2011, PMID 21378157].