Here's why:

* Chemical properties describe how a substance reacts with other substances. Toxicity involves a biological interaction, not simply a chemical reaction.

* Physical properties describe a substance's appearance, smell, taste, density, melting point, etc. Toxicity involves the effect on a living organism, which is not a physical property.

Toxicity is a biological property that describes a substance's ability to cause harm to a living organism. It depends on several factors, including:

* The nature of the substance: Some substances are inherently toxic, while others are only toxic in certain doses or forms.

* The dosage: Even non-toxic substances can become toxic in high doses.

* The route of exposure: The way a substance enters the body (inhalation, ingestion, skin contact) influences its toxicity.

* The individual's susceptibility: Factors like age, health, genetics, and even the presence of other substances can influence how toxic a substance is.

Therefore, toxicity is a complex concept that encompasses biological, chemical, and physical aspects, but it's not reducible to a single property.