Helium is a pure substance
Helium gas is a pure substance
Neither. Helium is not a mixture at all, it is a pure substance.
Neither. Helium is not a mixture at all, it is a pure substance.
No. Helium is an element, which makes it a pure substance.
Helium gas is a pure substance
Helium gas is a pure substance
Helium is pure as it is on the periodic table.
Helium is an element (and therefore a pure substance) yes
In theory it is a pure element. However, due the the cost of obtaining really pure helium, it is likely to contain trace amounts of other gases.
No. It will be a homogeneous mixture of gases.
Yes, it is a pure substance but can be mixed with other gases.
Helium is a gas, except at extremely cold temperatures.