**Core Concept**
Lithium is a mood stabilizer primarily used in the treatment of bipolar disorder. Its therapeutic effects are thought to be related to its ability to modulate neurotransmitter release and synaptic plasticity.

**Why the Correct Answer is Right**
Lithium has been shown to decrease suicidal tendencies in patients with bipolar disorder by modulating the serotonin system. It increases the expression of neurotrophic factors, such as brain-derived neurotrophic factor (BDNF), which promotes neuronal survival and differentiation. Lithium also inhibits the inositol signaling pathway, which is involved in the regulation of mood and behavior. This leads to a decrease in the activity of the hyperactive neurons, thereby reducing the risk of suicidal behavior.

**Why Each Wrong Option is Incorrect**
**Option A:** Fluoxetine is an SSRI, primarily used as an antidepressant. While it may be used in the treatment of bipolar depression, it is not the primary choice for managing suicidal tendencies in manic bipolar disorder.
**Option C:** Carbamazepine is an anticonvulsant and mood stabilizer, but it is not as effective as lithium in reducing suicidal tendencies in bipolar disorder.
**Option D:** Risperidone is an atypical antipsychotic, often used in the treatment of acute manic episodes, but it is not primarily used for managing suicidal tendencies.

**Clinical Pearl / High-Yield Fact**
Lithium is unique in its ability to reduce the risk of suicidal behavior in bipolar disorder. This is an important consideration when choosing a mood stabilizer for patients with a history of suicidal tendencies.

**✓ Correct Answer: B. Lithium**