Question: What is in helium gas that makes our voices go so high pitched?

Ben Mulhearn answered on 16 Mar 2018:

Helium is really light compared to the air we breathe, which is mostly nitrogen. Helium has a mass of 4, whereas nitrogen is 14. This means that when you produce your voice, the sound can travel through the helium much faster, which makes is ‘sound’ as though your voice is much higher than what it is!