Answer: A) numbers of neutrons Explanation: Isotopes are variations of an element that have the same charge as the original element, but a different mass, which is caused by either more/less neutrons in the nucleus.

Answer: A) Sulphur dioxide Explanation: Air pollutants are solid particles, gases, and liquid droplets in the air that can adversely affect ecosystems and the health of humans.   Major ambient air pollutants include toxic metals, polycyclic aromatic hydrocarbons, benzene, particulate matter (PM), nitrogen oxides, sulfur oxides, carbon monoxide, and ozone. Power plants, factories, and vehicle and air traffic are the most important anthropogenic sources of air pollution.   In addition, natural sources such as wildfires and volcanic activity contribute to ambient air pollution.