Explanation:
Concept overview / definitionAtmospheric pressure is the force exerted by the weight of air above a given point. As you go higher, the column of air above you becomes shorter and less dense, changing the pressure you experience.
Why the correct option is correctWith increasing altitude, there is less air overhead, so the weight of the air column reduces. This is why pressure at higher elevations is lower than near the reference surface level, and many weather and human physiology effects are tied to this decrease.
Why the other options are incorrectPressure does not increase with altitude because air density and overlying air mass reduce upward. Saying pressure stays constant ignores the basic vertical structure of the atmosphere. Statements claiming pressure changes only with temperature are incomplete; temperature can influence pressure, but height alone changes air mass above a point.
UPSC exam tip / common confusionUPSC may combine altitude with temperature and pressure in options. Do not memorize blindly; anchor your logic in “air column weight.” If the air above you is less, pressure must be less, even if local temperatures vary.
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