The correct answer is option 4, Ozone. Ozone is a gas that is naturally present in the Earth`s atmosphere. It is formed when oxygen molecules (option 1) are split apart by ultraviolet (UV) radiation from the Sun. Ozone molecules then absorb a significant amount of UV radiation, particularly that in the shorter wavelength range known as UV-C and most of the UV-B radiation. This absorption process acts as a filter, protecting the Earth`s surface, including living organisms, from the harmful effects of excessive UV radiation.

Option 2, Nitrogen, is the most abundant gas in the Earth`s atmosphere and does not significantly filter out UV radiation. Option 3, Helium, is also not involved in the filtration of UV radiation.

It`s important to note that although oxygen and ozone play a role in absorbing UV radiation, ozone is particularly effective. Therefore, option 4, Ozone, is the most accurate answer.