Rationale: A. Prepare an IV bolus of dextrose 5% in water: Administering dextrose does not reverse magnesium sulfate toxicity. Dextrose primarily provides energy and fluid but has no effect on magnesium levels or neuromuscular function. B. Administer methylergonovine IM: Methylergonovine is used to treat postpartum hemorrhage by promoting uterine contractions. It does not counteract magnesium toxicity and is unrelated to this emergency situation. C. Administer calcium gluconate IV: Calcium gluconate is the antidote for magnesium sulfate toxicity. It works by antagonizing magnesium at neuromuscular junctions, reversing respiratory depression, hypotonia, and loss of deep tendon reflexes associated with toxicity. D. Position the client supine: While client positioning may assist with comfort or circulation, supine positioning does not treat magnesium sulfate toxicity. The priority is administering the antidote to prevent further complications such as respiratory arrest.