Which of the following substances has been determined to pose the most significant potential threat to human health in terms of frequency of contact, toxicity and potential for human exposure? a. Polycyclic aromatic hydrocarbons (from petroleum)
b. Arochlor (a pesticide)
c. Chloroform
d. Arsenic

Polycyclic aromatic hydrocarbons (from petroleum)

Explanation:

Polycyclic aromatic hydrocarbons (PAH) is a group of compounds which contain more than one aromatic ring. Typically examples include; naphthalene, anthracene, phenanthrene etc.

PAH are present in petroleum products. Almost everyone is regularly exposed to vehicles or other equipments that uses petroleum products as fuel. PAH is usually released from the combustion engine of these equipments and may be inhaled by humans. Thus there is a very high risk of PAH exposure compared to other items listed in the question.

PAHs are known to cause different kinds of cancer and other types of health issues in the body. The most disturbing toxicity of PAH is its carcinogenicity which makes it a very serious potential health risk for humans exposed to it on regular basis.

a  solution  is always transparent, light passes through with no scattering from solute particles which are molecule in size. the  solution  is homogeneous and does not settle out. a colloid is intermediate between asolution  and a  suspension. while asuspension  will separate out a colloid will not.