Multiple choice

Why are there fewer molecules of air up in the mountains?

  1. because air pressure increases as you go higher

  2. because air pressure is the same in all layers of atmosphere

  3. because air is too heavy

  4. because air pressure decreases as you go higher
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Gravity pulls air molecules down toward Earth's surface, meaning air pressure and density are highest at sea level. As you ascend a mountain, there is less atmosphere above you, so air pressure decreases and the air molecules spread out.

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