About IS !!

Is it really test tubes of gases inverted?
It is true that if the test tube contains gas less dense that air, then it will be inverted
Because if gas are denser than air, is floats. If test tube stands upwards, the gas may escape through some space at the opening
If it is inverted, even it floats in the test tube, the upper end is glass with no space to escape. This can prevent gas leakage
This method is called upward delivery

But for gases denser than air
We use downward delivery
that is the test tube stands upright
because denser gas sikns at the bottom
This is again used to prevent gas leakage