Choose the word which is different from the rest.

Troposphere, Stratosphere, Mesosphere, Thermosphere, and Exosphere are the five main layers of the Earth's atmosphere classified based on temperature gradients.

Troposphere is the lowest layer where weather changes occur.

Stratosphere lies above the troposphere and contains the ozone layer.

Thermosphere is characterized by high temperatures due to solar radiation absorption.

Exosphere is the outermost layer where the atmosphere merges with space.

Ionosphere, however, is not a separate layer based on temperature. It is a region of the atmosphere that spans across parts of the mesosphere and thermosphere.

It is defined by the ionization of particles due to solar and cosmic radiation, which makes it electrically charged and capable of reflecting radio waves.

Thus, unlike the others, the ionosphere is classified by electrical properties, not temperature layers, making it different from the rest.