Asubstance can be pure: when a substance has unique properties through which it can be distinguished when a substance has common properties through which it can be identified when a substance can be separated into two different groups of material when a substance can be broken down into basic parts

14,16 18 reacts with group

the ozone layer acts as a filter for the shorter wavelength and highly hazardous ultraviolet radiation (uvr) from the sun, protecting life on earth from its potentially harmful effects. when the sky is clear, there is an inverse relationship between stratospheric ozone and solar uvr measured at the earth's surface.