How do the masses of subatomic particles compare on a relative basis? do the proton and neutron have exactly the same mass?

The  electron has a mass of 1/1840 of a proton or neutron. Protons and neutrons have the same mass.

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.

a compound is a molecule made of atoms from different elements.

a. by the combination of an unlimited number of elements