Can anyone please explain ,how the ozone layer or ozone molecules protect the earth from UVR? I expect very detail scientific explanation like the activities of molecules step by step.

The ozone layer in the stratosphere absorbs a portion of the radiation from the sun, preventing it from reaching the planet's surface. Most importantly, it absorbs the portion of UV light called UVB. UVB is a kind of ultraviolet light from the sun (and sun lamps) that has several harmful effects.

About ozone and its structure: Ozone or in proper words 'ozone gas' is an allotrope of oxygen and of molecular formula O3. It stabilize itself through continuous resonance of electron (lone pairs of oxygen) between the three oxygen atoms.

Function, working and importance of Ozone layer: Ozone layer is present in the upper part of Stratosphere where it continuously absorbs the harmful ultra-violet (UV) rays of sun and prevent it from reaching the earth. The oxygen molecules present in the Stratosphere absorb the high energy UV rays and breaks into two oxygen atoms. Since oxygen atom is highly unstable, so it binds with the oxygen molecule and forms ozone molecule. Again, the ozone molecule absorbs the UV rays and breaks down into one oxygen molecule and oxygen atoms. This is continuous process which goes on and on in the upper part of Stratosphere absorbing all the UV rays.

Ultra- violet rays are very high energy waves which can completely damage the whole DNA of an organism if exposed and it can cause skin cancer, blindness, thickening of cornea and many more. So the ozone layer protects the earth from all these problems by continuous absorbing the UV rays and only allowing the visible rays to enter earth atmosphere. But due to excessive pollution, the ozone layer is becoming thin which is a very serious problem. The thickness of the ozone layer is measured in Dobson unit (DU).

Ozone gas are also used in mineral water where it breaks downs in oxygen molecules in water.