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.

substituting a hydrogen atom with a halogen in a hydrocarbon:

- the single bond remains single. a is wrong.

- the bond with hydrogen is as strong as with a halogen. c is wrong

- a hydrocarbon is saturated if there is no double bond. we do not know that so d is wrong.

- carbon will always have four valence electrons. e is wrong.

by elimination, the correct answer is b. the boiling point of the new compound increases.