Which type of poison is characterized by the presence of "Mees lines" on nails?

Mees lines are transverse white lines that appear across the entire nail plate and can be indicative of certain types of poisoning. The correct association of Mees lines with arsenic is significant because arsenic is known to disturb keratinization processes, which can lead to these characteristic changes in the nails. The formation of Mees lines signifies a temporary interruption in nail growth, often linked to systemic illnesses, including arsenic poisoning.

In the case of the other substances, such as cyanide, lead, and carbon monoxide, while these can also lead to severe health effects, they do not produce Mees lines as a specific indicator. Cyanide tends to disrupt cellular respiration, lead can cause a variety of systemic manifestations but is more commonly associated with basophilic stippling of red blood cells, and carbon monoxide primarily causes hypoxic injuries that are not associated with changes in nails. Thus, the presence of Mees lines serves as a specific marker for arsenic poisoning, making it the correct answer.