The client is in a manic phase of bipolar disorder, and is receiving lithium. What will the nurse expect to assess when the client's lithium level is 0.3 mEq/L?

The correct answer is D: Hyperactivity. At a lithium level of 0.3 mEq/L, the client is likely to exhibit symptoms of hyperactivity due to subtherapeutic levels of lithium. This is because lower lithium levels may not effectively control the manic symptoms in bipolar disorder. Sleepiness (A), relaxed appearance (B), and calm behavior (C) are more indicative of sedative effects often seen at higher, toxic levels of lithium, not at 0.3 mEq/L. Therefore, hyperactivity is the most likely assessment finding at this particular lithium level.