Inhalation toxicity assesses how poisonous a pesticide is when:

Inhalation toxicity specifically evaluates the potential harm a pesticide can inflict when it is inhaled or breathed into the lungs. This form of toxicity is critical to understanding because the respiratory system can absorb substances rapidly into the bloodstream, potentially leading to severe health effects. Knowledge of inhalation toxicity helps in ensuring proper handling and application methods are used to prevent respiratory exposure to pesticides, thereby protecting the health of applicators and bystanders.

The other options pertain to different routes of exposure, such as dermal (skin contact) or ingestion (through food), which are assessed through other types of toxicity evaluations, but do not relate specifically to inhalation. Understanding each route of exposure is essential for comprehensive pesticide safety.