an open flask of air is heated. at low or high temperature does the flask contain gas molecules? explain.?

Answer 1

Well... as long as the flask remains open, there will be gas molecules in it irrespective of the temperature. The thing is that when the flask is heated, the kinetic energy of the gas molecules will increase and hence most of the gas molecules will tend to escape from the flask. However, a vaccuum is never created (i.e. the flask is never devoid of gas molecules) because a convection current of gas will be set up and the cooler air surrounding the flask will enter the flask.
( note : this condition holds good only as long as the flask remains open.)

Answer 2

At Any internal pressure, the flask contains gas molecules.
The question should probably be, at high or low temperature does the flask contain more gas molecules.

The flask has a given volume which we will assume is unchanged by heating the container.
As the gas's temperature within the container rises, the gas expands to take up a larger volume...this means than some of the gas molecules will 'over-flow' the container and 'spill-out'.
When the temperature is lowered, the gas inside the container contract and more gas can flow into the container, so more gas molecules enter.

Although the volume of gas inside the container is always the same, the number of molecules of gas is less when the temperature is higher.

Ideal gas law,
PV = nRT

Answer 3

yes.
heating air does not create a vacuum, so gas molecules will remain.