Final answer:
Hyporeflexia is indicative of magnesium toxicity in a client receiving magnesium sulfate, reflecting decreased neuromuscular transmission and reduced nervous system activity similar to hypercalcemia symptoms.
Step-by-step explanation:
The clinical manifestation that a nurse should recognize as indicative of magnesium toxicity in a client receiving magnesium sulfate is hyporeflexia (b). Magnesium toxicity can lead to decreased neuromuscular transmission. This results in symptoms that are reflective of reduced nervous system activity, similar to what is observed in hypercalcemia, where symptoms include lethargy, sluggish reflexes, and in severe cases, coma. An excess of magnesium in the body can suppress the central nervous system, leading to decreased reflexes, muscle weakness, and in severe cases, respiratory failure and cardiac arrest. This is in stark contrast to hyperactivity and increased muscle strength, which are not associated with magnesium toxicity.