Option 1 -> The ionosphere is an upper atmospheric region characterized by ionized particles, not where the protective ozone layer is concentrated.
Option 2 -> The troposphere is the lowest atmospheric layer where weather occurs and where we live, but the ozone layer is not located here.
Option 3 -> The stratosphere contains the ozone layer at approximately 15-35 km altitude, where ozone (O₃) molecules absorb harmful UV radiation.
Option 4 -> The mesosphere is above the stratosphere and is not where the primary ozone concentration that protects Earth is found.
Hence, Option 3: Stratosphere -> The ozone layer sits in the stratosphere, forming a protective shield that absorbs 97-99% of the Sun's harmful ultraviolet radiation, making life on Earth possible -> correct