Which among the following clouds occur at the highest altitude?

Answer: [D] Noctilucent

Night clouds or noctilucent clouds, made of crystals of water ice, re most commonly observed in the summer months at latitudes between 50° and 70° north and south of the equator. They can only be observed when the Sun is below the horizon. They are the highest clouds in Earth’s atmosphere, located in the mesosphere at altitudes of around 76 to 85 kilometres (47 to 53 mi). They are normally too faint to be seen, and are visible only when illuminated by sunlight from below the horizon while the lower layers of the atmosphere are in the Earth’s shadow. Noctilucent clouds are not fully understood and are a recently discovered meteorological phenomenon; there is no record of their observation before 1885.

This question is a part of GKToday's Integrated IAS General Studies Module