The Ozone layer which is present in the Earth's atmosphere protects it by restricting from UV or Ultraviolet radiation, the dangerous rays contained by Sun.
The reduction potential of hydrogen half-cell will be negative if : (1) = 2 atm and [H+] = 2.0 M (2) = 1 atm and [H+] = 2.0 M (3) = 1 atm and [H+] = 1.0 M (4) = 2 atm and [H+] = 1.0 M