**Core Concept**
Neurotic depression, also known as dysthymia or neurotic anxiety depression, is a type of depressive disorder characterized by persistent low mood, anxiety, and somatic complaints. It often co-exists with anxiety disorders and can be distinguished from endogenous depression by its lack of significant weight loss or gain, psychomotor retardation, or other severe vegetative symptoms.

**Why the Correct Answer is Right**
In neurotic depression, patients may exhibit an increase in appetite, leading to weight gain (Option D), which is a common feature. However, increased libido (Option C) is not typically associated with neurotic depression. In fact, decreased libido is more commonly observed in patients with depression. The correct answer also includes Ravenous appetite (Option A), which is a characteristic of neurotic depression. Option B, Hypersomnia, is also associated with neurotic depression, as patients often experience disturbed sleep patterns, including hypersomnia.

**Why Each Wrong Option is Incorrect**
**Option C:** Increased libido is not typically associated with neurotic depression, and decreased libido is more commonly observed in patients with depression.
**Option D:** Weight gain is a characteristic of neurotic depression, not weight loss, which is more commonly associated with endogenous depression.

**Clinical Pearl / High-Yield Fact**
In psychiatry, it's essential to differentiate between endogenous and neurotic depression, as their treatment approaches and prognoses differ. Neurotic depression often responds well to psychotherapy and behavioral interventions, whereas endogenous depression may require pharmacotherapy.

**✓ Correct Answer: A. ac. Both Ravenous appetite and Increased libido are incorrect characteristics of neurotic depression.**