D) physical and chemical changes
Answer:
New substances are produced by a chemical change
"The inert gases are obtained by fractional distillation of air, with the exception of helium which is separated from a few natural gas sources rich in this element, through cryogenic distillation or membrane separation. For specialized applications, purified inert gas shall be produced by specialized generators on-site. They are often used by chemical tankers and product carriers (smaller not a big as well as the tendency of inert gases vesselshtop specialized generators are also available for laboratories."
