What gas is inside the bubbles we sometimes see in an ice cube?
Do you mean the bubbles that you often observe the in an ice cube?
And we presume that this is simply air. When a compound solidifies, it (often) expels the molecules that are dissolved in it. Air (as a gaseous mixture) is always dissolved in the water we drink. When water freezes it can expel the gases it has dissolved in solution.
I apologize if I have missed the point of your question.