Which of the following is classified as a volatile organic compound?

Dichloromethane, also known as methylene chloride, is categorized as a volatile organic compound (VOC) due to its chemical properties. VOCs are organic chemicals that can easily evaporate at room temperature, contributing to air pollution and potential health effects. Dichloromethane has a relatively low boiling point, which allows it to readily vaporize, making it classified in this manner.

In contrast, substances like calcium, sodium, and zinc are not organic compounds and do not possess the volatilities that characterize VOCs. They are inorganic elements and do not contribute to the same environmental or health concerns associated with volatile organic compounds. By understanding these distinctions, it becomes clear why dichloromethane is recognized as a VOC while the others are not.