Multiple choice

A balloon filled with helium rises in air because __________.

  1. air exerts an upward force on the balloon

  2. the balloon is weightless

  3. helium is less dense than air

  4. helium pushes down on the air below the balloon

  5. all of these

Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A helium balloon rises because helium is less dense than air, which contains oxygen and nitrogen. Helium is a lighter and smaller molecule than both oxygen and nitrogen.