Final answer:
The atmospheric layers of Neptune include the uppermost methane ice clouds, followed by layers potentially made of hydrogen sulfide ice and deeper still, ammonium hydrosulfide ice. Beneath the ice layers lies the stratosphere, being the coldest part, and possibly lower still, layers of water ice.
Step-by-step explanation:
The various atmospheric layers for Neptune can be properly labeled based on the composition of ice particles and gases present at different levels. The upper clouds of Neptune, according to provided information, are composed of methane ice crystals that form at a temperature of 70 K and a pressure of 1.5 bars in the troposphere. This thin cloud layer is situated above another cloud layer, potentially composed of hydrogen sulfide ice particles at a pressure of 3 bars. Beneath these layers, ammonium hydrosulfide ice clouds may exist deeper within the atmosphere. Above the troposphere, which contains these ice layers, is the stratosphere, considered the coldest part of Neptune's atmosphere. Notably, Neptune has less haze than Uranus and exhibits a pale blue color due to the scattering of sunlight by gas molecules in its atmosphere.
As the outer layers of Neptune's atmosphere contain hydrogen and helium gas, and since it is more common to find frozen water at deeper levels, it is probable that a layer of water ice exists below the ammonium hydrosulfide and hydrogen sulfide ice layers. The mentioned ice formations within Neptune's atmosphere contribute to the active cloud patterns and distinct atmospheric dynamics that characterize this ice giant, reflecting the diverse and complex climate system on this distant planet.