Here's why:

* Hydrogen (H2) and neon (Ne) are both elements, meaning they cannot be broken down into simpler substances.

* They are both gases at room temperature.

* When mixed, they don't react chemically with each other. They simply occupy the same space as individual gas molecules.

Think of it like mixing air. Air is a mixture of different gases, including nitrogen, oxygen, and a tiny amount of argon. Just like air, a mixture of hydrogen and neon wouldn't create a new substance.