MPSC 2026 Prelims Paper-I · Question 26 of 100

Correct — option (3), '(c), (g), (e), (d), (a), (f), (b)'. The atmosphere above any point on the earth is built as an alternating stack: a layer, then the boundary that caps it, then the next layer, then its boundary, and so on. Every name ending in -sphere is a layer and every name ending in -pause is the ceiling of the layer whose root it shares. Read upward from the ground the sequence is therefore troposphere, tropopause, stratosphere, stratopause, mesosphere, mesopause, thermosphere — that is (c), (g), (e), (d), (a), (f), (b), which is exactly option (3). Two independent checks confirm it. The first is the naming rule: the tropopause must come immediately after the troposphere and before the stratosphere, the stratopause immediately after the stratosphere, the mesopause immediately after the mesosphere, and only option (3) keeps all three pairings intact. The second is the temperature profile, which is what these boundaries were defined by in the first place. In the troposphere temperature falls with height at roughly 6.5 degrees Celsius per kilometre; at the tropopause the fall stops. Through the stratosphere temperature rises with height, because ozone there absorbs ultraviolet radiation and warms the air from above; the rise ends at the stratopause. Through the mesosphere temperature falls again, reaching the lowest values found anywhere in the atmosphere at the mesopause. Above that, in the thermosphere, temperature climbs steeply again as the thin gas absorbs the shortest-wave solar radiation. Fall, rise, fall, rise — four regimes separated by three pauses. The fastest way to solve this question in the hall does not require any of that detail: the stem says 'ascending order from the earth's surface', so whatever stands first must be the layer touching the ground, and only option (3) begins with (c), the troposphere. The other three begin at the tropopause, at the mesosphere and at the stratosphere respectively, and can be struck out in a single glance.

• (1)(g), (c), (d), (e), (b), (f), (a) — Begins with (g), the tropopause, placing a boundary below the layer it caps — the ceiling of the troposphere cannot lie beneath the troposphere. It then compounds the error by putting the stratopause (d) before the stratosphere (e), inverting the same relationship a second time, and it ends with the thermosphere buried in the middle while the mesosphere is pushed to the top of the atmosphere. A candidate who applies the single test 'what touches the ground' rejects this option before reading past its first entry.
• (2)(a), (f), (b), (g), (c), (d), (e) — Starts at the mesosphere, roughly 50 km up, and only reaches the troposphere in fifth place — so the layer holding almost all the atmosphere's mass, its water vapour and all its weather is stacked above the thermosphere. The internal pairings are partly sound, mesosphere-mesopause and troposphere-stratopause aside, which is what makes it tempting to a candidate who is checking pairs without checking the base. Order questions must be anchored at one end first; here the anchor is the ground.
• (4)(e), (d), (a), (g), (c), (b), (f) — Starts at the stratosphere and omits the troposphere from the base entirely, dropping it into fifth place immediately after the tropopause. This is the most plausible-looking of the three wrong options because its first three entries — stratosphere, stratopause, mesosphere — are in genuinely correct relative order; the error is that this correct fragment has been placed at the bottom of the stack instead of in the middle. It is a reminder that a correct sub-sequence proves nothing about the whole.

The atmosphere is divided vertically by how temperature behaves with height, not by composition, because up to about 80 km the gases are well mixed and composition alone would give no boundaries at all. Four regimes are recognised. The troposphere, extending from the surface to roughly 8 km over the poles and 18 km over the equator, is heated from below by the earth's surface, so temperature falls with height at an average lapse rate of about 6.5 degrees per kilometre; it holds roughly three-quarters of the atmosphere's mass, nearly all its water vapour, and all its weather. The stratosphere, reaching to about 50 km, is heated from above by ozone absorbing ultraviolet radiation, so temperature rises with height, which makes it stable, cloudless and largely free of turbulence — the reason long-haul jets cruise in its lower part. The mesosphere, to about 80 km, has no such heat source and cools with height to the lowest temperatures in the whole atmosphere; it is dense enough to burn up most incoming meteors. Above the mesopause the thermosphere absorbs extreme ultraviolet and X-radiation and its temperature rises steeply, though the gas is so rarefied that the heat content is negligible. Each regime is closed by a 'pause' — tropopause, stratopause, mesopause — at which the temperature trend reverses.

The vertical structure is not a piece of trivia; it explains a string of facts that MPSC and UPSC both examine. Weather is confined to the troposphere because that is where the water vapour and the convection are, and the tropopause acts as a lid that thunderstorm anvils spread out against. The ozone layer, concentrated between roughly 15 and 35 km, sits in the stratosphere, which is why ozone depletion is a stratospheric problem while photochemical smog is a tropospheric one, and why the two must never be conflated. Radio communication over long distances depends on the ionised layers within the thermosphere, which reflect certain radio waves back to earth. The troposphere's thickness varies with latitude and with season — thicker over the equator because vigorous convection pushes the lid higher, thinner over the poles — which is a standard follow-up question. The Marathi column of this paper uses the Sanskritic terms throughout: तपांबर for troposphere, तपस्तब्धी for tropopause, स्थितांबर for stratosphere, स्थितस्तब्धी for stratopause, मध्यांबर for mesosphere and मध्यस्तब्धी for mesopause, with थर्मोस्फिअर transliterated.

• Troposphere: surface to about 8 km at the poles and 18 km at the equator. Temperature falls with height at a normal lapse rate of about 6.5 degrees Celsius per kilometre. It contains roughly three-quarters of atmospheric mass, almost all water vapour and dust, and every weather phenomenon.
• Tropopause: the ceiling of the troposphere, where the fall in temperature stops. It is coldest over the equator, around minus 80 degrees Celsius, and warmer over the poles, around minus 45 degrees Celsius — the opposite of surface temperatures, because the equatorial tropopause stands so much higher.
• Stratosphere: from the tropopause to about 50 km. Temperature rises with height because ozone, concentrated between roughly 15 and 35 km, absorbs ultraviolet radiation. The absence of water vapour, cloud and convection makes it stable and smooth, which is why jet aircraft cruise in its lower reaches.
• Mesosphere: from the stratopause at about 50 km to the mesopause at about 80 km. Temperature falls with height throughout, reaching the lowest values found anywhere in the atmosphere at the mesopause. Most meteors entering the atmosphere burn up in this layer.
• Thermosphere: above about 80 km, where temperature rises steeply with height as the extremely thin gas absorbs short-wave solar radiation. The ionosphere lies within it, and its ionised layers reflect radio waves back to the earth, making long-distance short-wave communication possible.

• Treating a 'pause' as a layer of its own rather than as a boundary. Each pause takes its name from the layer beneath it and lies at that layer's top, so tropopause follows troposphere, stratopause follows stratosphere and mesopause follows mesosphere — three fixed pairs that decide most ordering questions on their own.
• Forgetting that temperature reverses direction at every pause. It falls in the troposphere, rises in the stratosphere, falls in the mesosphere and rises in the thermosphere; a candidate who remembers 'it just keeps getting colder with height' will misplace both the stratosphere and the thermosphere.
• Assuming the troposphere has a fixed thickness. It is roughly 18 km deep over the equator and about 8 km over the poles, and it is deeper in summer than in winter, because the depth is set by how far convection can push the lid.

Atmospheric structure is asked in four recognisable ways. First, the ordering question used here, which is solved by anchoring at the ground and applying the sphere-pause pairing rule. Second, the property-to-layer match — where weather occurs, where ozone lies, where meteors burn, where radio waves are reflected — which is pure recall of one line per layer. Third, the reasoning question on why temperature rises in the stratosphere but falls in the troposphere, where the expected answer names the heat source in each case. Fourth, numerical questions on the lapse rate or on tropopause temperature. Note the examiner's device in this paper: seven items rather than the usual four, which makes exhaustive checking slow. Ordering questions with many items are always attacked from one end, never by verifying whole sequences.

No directly related past PYQ was found.

• practice — not a real PYQ

  In which layer of the atmosphere does temperature increase with height, and what is the reason for that increase ?

  • (a)Troposphere — heating of the air by the earth's surface
  • (b)Stratosphere — absorption of ultraviolet radiation by ozone
  • (c)Mesosphere — friction from incoming meteors
  • (d)Tropopause — the constant temperature of the boundary

  Answer(b) Stratosphere — absorption of ultraviolet radiation by ozone. Ozone concentrated roughly between 15 and 35 km absorbs ultraviolet and warms the air from above, so temperature rises with height and the layer is stable, cloudless and free of turbulence. In the troposphere the heat source is the ground below, so temperature falls with height instead.

• practice — not a real PYQ

  The lowest temperatures anywhere in the earth's atmosphere are recorded at which level ?

  • (a)Tropopause
  • (b)Stratopause
  • (c)Mesopause
  • (d)Upper thermosphere

  Answer(c) Mesopause — the ceiling of the mesosphere at about 80 km, where the temperature fall through that layer bottoms out before the steep rise of the thermosphere begins. The tropopause is cold but not the coldest, the stratopause is a temperature maximum rather than a minimum, and the thermosphere is the hottest region by temperature though its gas is far too thin to hold much heat.