**Core Concept**
Depression with suicidal tendencies is a severe mental health condition that requires immediate and effective treatment to prevent harm to the patient. The treatment of choice should ideally address both the depressive symptoms and the suicidal tendencies, thereby reducing the risk of self-harm.

**Why the Correct Answer is Right**
The treatment of choice in depression with suicidal tendencies is hospitalization and initiation of electroconvulsive therapy (ECT) or pharmacotherapy with lithium or a combination of a mood stabilizer and an antipsychotic. This approach helps to rapidly alleviate depressive symptoms and reduce the risk of suicidal behavior. Lithium has a well-established efficacy in treating depression, particularly in patients with suicidal tendencies. It acts by inhibiting the reuptake of serotonin and norepinephrine, thereby increasing their availability in the synaptic cleft.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as selective serotonin reuptake inhibitors (SSRIs) alone may not be sufficient to manage severe depression with suicidal tendencies, especially in the acute phase.
**Option B:** This option is incorrect as benzodiazepines are not a primary treatment for depression and can even exacerbate suicidal behavior in some cases.
**Option C:** This option is incorrect as atypical antipsychotics may be used as adjunctive therapy but are not the first-line treatment for severe depression with suicidal tendencies.

**Clinical Pearl / High-Yield Fact**
Lithium is a mood stabilizer that has a narrow therapeutic index, and its serum levels should be monitored regularly to avoid toxicity.

**Correct Answer:** D.