What is the appropriate serum lithium level for maintenance and safety?

Choice A reason: This is incorrect because 50-100 mEq/L is far above the therapeutic range and would be toxic. Choice B reason: This is incorrect because 10-50 mEq/L is also excessively high and unsafe. Choice C reason: This is correct because the therapeutic serum lithium level for maintenance is 0.5-1.5 mEq/L. Levels above 1.5 mEq/L increase the risk of toxicity, while levels below 0.5 mEq/L may be ineffective for mood stabilization. Choice D reason: This is incorrect because 0.1-1 mEq/L is too low, with the lower end being subtherapeutic.