**Core Concept**
Lead poisoning occurs when there is excessive accumulation of lead in the body, causing various systemic effects. The most common mode of lead poisoning is through inhalation of lead particles, which can arise from occupational exposure in industries such as construction, mining, and manufacturing.

**Why the Correct Answer is Right**
The correct answer is inhalation, as it is the primary route of exposure for lead poisoning. When lead particles are inhaled, they can be deposited in the lungs and then absorbed into the bloodstream, leading to systemic toxicity. This can occur through the use of lead-based products, such as lead paint or lead-glazed ceramics, which can release particles into the air when disturbed. The inhaled lead particles can also be carried to the brain, causing neurological damage.

**Why Each Wrong Option is Incorrect**
**Option A:** Ingestion is a possible route of lead poisoning, but it is not the most common mode. Ingestion typically occurs through the consumption of contaminated food or water, which is less common than inhalation exposure.
**Option B:** Dermal exposure is not a significant route of lead poisoning. While lead can be absorbed through the skin, this route is not as efficient as inhalation or ingestion.
**Option C:** Parenteral exposure is not a relevant route of lead poisoning. Lead is not typically administered through injections or other parenteral routes.

**Clinical Pearl / High-Yield Fact**
Lead poisoning can cause a range of symptoms, including abdominal pain, constipation, and encephalopathy. It is essential to recognize the risk factors for lead exposure, such as occupational or environmental exposure, and to perform regular blood tests to detect elevated lead levels.

**Correct Answer: C.**