NDA (II) 2021 General Ability Test · Question 64 of 149

Correct — B, Troposphere, Stratosphere, Mesosphere, Thermosphere. Starting at the ground and moving up, the atmosphere is layered as the troposphere (where weather occurs), the stratosphere (which holds the ozone layer), the mesosphere (where meteors burn up) and the thermosphere (where temperature rises sharply and auroras form). A simple memory aid is 'The Sky Must Trap' for Tropo, Strato, Meso, Thermo.

• (a)Troposphere, Stratosphere, Thermosphere, Mesosphere — The first two are right, but the mesosphere lies below the thermosphere, not above it, so the last two layers are swapped.
• (c)Thermosphere, Mesosphere, Stratosphere, Troposphere — This is the correct order reversed — it lists the layers from the top of the atmosphere downwards, not upwards from the surface.
• (d)Stratosphere, Mesosphere, Troposphere, Thermosphere — It wrongly starts with the stratosphere and buries the troposphere in the middle, yet the troposphere is the lowest layer, touching the surface.

The atmosphere is divided into concentric layers by the way temperature changes with height. From the surface upward they are the troposphere, stratosphere, mesosphere, thermosphere and exosphere. Temperature falls through the troposphere, rises through the stratosphere because ozone absorbs ultraviolet rays, falls again through the mesosphere and rises steeply in the thermosphere.

Every distractor keeps a couple of layers in place but shuffles the mesosphere and thermosphere or reverses the whole order. Anchoring on the idea that the troposphere is where we live and weather happens fixes the bottom, and remembering that the ozone-bearing stratosphere sits just above it settles the sequence.

• The troposphere holds most of the atmosphere's mass and nearly all weather, reaching about 8 km at the poles and 18 km at the equator.
• The stratosphere contains the ozone layer, which absorbs ultraviolet radiation and warms the layer.
• Meteors typically burn up in the mesosphere, the coldest atmospheric layer.
• The thermosphere is where auroras occur and many satellites orbit, and its temperature can exceed 1,000 degrees Celsius.

• Swapping the mesosphere and thermosphere — the mesosphere is the third layer up, the thermosphere the fourth.
• Reading the options from the top down instead of from the surface up.

Asked as a straight ordering of atmospheric layers, sometimes with the sequence reversed as a trap.

No directly related past PYQ was found.

• practice — not a real PYQ

  In which atmospheric layer does almost all weather occur?

  • (a)Troposphere
  • (b)Stratosphere
  • (c)Mesosphere
  • (d)Thermosphere

  Answer(a) Troposphere — it holds most water vapour, and clouds and weather form there.

• practice — not a real PYQ

  The ozone layer that absorbs ultraviolet radiation lies in the

  • (a)troposphere
  • (b)stratosphere
  • (c)mesosphere
  • (d)thermosphere

  Answer(b) stratosphere.