Multi-select: Knowing that "when a gas in an open container evaporates, that gas spreads out into the air", how would one answer "A balloon is filled with Helium, and then is opened and pressed up to someone's mouth to make a voice high, why does it do this?"

Options:
[+] gas fills the new area;
[+] gas easily is dispersed;
[+] gas moves around freely;
[+] gas is lighter than air;...A:
gas fills the new area