**Core Concept**
Thyrotoxicosis, often caused by hyperthyroidism, is a condition characterized by an excess of thyroid hormones in the body. This can lead to various clinical manifestations, including tachycardia, tremors, and weight loss. Differentiating thyrotoxicosis from anxiety neurosis, a psychological condition, is crucial for proper diagnosis and treatment.

**Why the Correct Answer is Right**
The sleeping pulse rate is a useful clinical indicator to distinguish between thyrotoxicosis and anxiety neurosis. In thyrotoxicosis, the resting or sleeping pulse rate is typically elevated, often above 100 beats per minute, due to the increased sympathetic activity caused by excess thyroid hormones. In contrast, individuals with anxiety neurosis usually have a normal sleeping pulse rate. This is because anxiety is primarily a psychological condition affecting the central nervous system, rather than a direct effect on the cardiovascular system.

**Why Each Wrong Option is Incorrect**
**Option A:** Tachycardia can be present in both thyrotoxicosis and anxiety neurosis, making it an unreliable differentiator.
**Option C:** Moist hands can be a symptom of thyrotoxicosis due to increased sweat gland activity, but it is not a specific enough indicator to rule out anxiety neurosis.
**Option D:** Ankle jerk reflex is not directly related to the differentiation between thyrotoxicosis and anxiety neurosis.

**Clinical Pearl / High-Yield Fact**
It is essential to note that a single clinical finding may not be sufficient to diagnose thyrotoxicosis or anxiety neurosis. A comprehensive history and physical examination, along with laboratory tests, are necessary to make an accurate diagnosis.

✓ Correct Answer: B. Sleeping pulse rate