**Core Concept**
The patient's symptoms, including paraesthesia, hyperkeratosis, and raindrop pigmentation, are indicative of a specific occupational exposure to a toxic substance. This condition is characterized by a triad of neurological, cutaneous, and mucosal manifestations, resulting from the accumulation of a particular toxin in the body.

**Why the Correct Answer is Right**
The patient's presentation is classic for Arsenic poisoning. Arsenic is a potent neurotoxin that can cause paraesthesia, numbness, and tingling in the hands and feet (Option D). The toxin also leads to hyperkeratosis, which is the thickening of skin, particularly on the palms and soles. Raindrop pigmentation, a result of arsenic deposition in the skin, is another characteristic finding in arsenic poisoning. Arsenic exposure can occur through contaminated water, food, or air, and is a significant public health concern in regions with poor environmental management, such as West Bengal.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect as it does not match the patient's symptoms. Lead poisoning, for example, can cause neurological symptoms, but it does not typically present with hyperkeratosis or raindrop pigmentation.
* **Option B:** This option is incorrect as it does not align with the patient's presentation. Mercury poisoning can cause neurological symptoms, but it does not typically cause hyperkeratosis or raindrop pigmentation.
* **Option C:** This option is incorrect as it does not match the patient's symptoms. Cadmium poisoning can cause kidney damage and bone disease, but it does not typically present with hyperkeratosis or raindrop pigmentation.

**Clinical Pearl / High-Yield Fact**
Arsenic poisoning can occur through various routes, including ingestion, inhalation, and dermal exposure. It is essential to consider the patient's occupation, environmental exposure, and dietary habits when suspecting arsenic poisoning. The patient's symptoms and history should prompt a thorough investigation, including laboratory tests and imaging studies, to confirm the diagnosis.

**Correct Answer:** D. Arsenic.