which process is a chemical change?\no breaking of glass\no formation of frost\no magnetization of an iron…

Brief Explanations:

A chemical change results in a new substance being formed. Breaking glass is a physical change as it only changes the shape of the glass. Formation of frost is a physical change (phase - change from gas to solid). Magnetization of an iron nail is a physical change as it doesn't change the chemical composition of iron. Loss of atmospheric ozone involves a chemical reaction where ozone ($O_3$) is broken down into other substances, so it is a chemical change.

Answer:

loss of atmospheric ozone