What will happen to gas in a closed container if the temperature is increased at a constant pressure

I'd think that the volume should increase, but the gas is in a closed container so it can't increase in volume.... I don't know what will happen?

If the volume of the container is fixed (e.g., a tightly stoppered bottle), then it would be impossible for the pressure to remain constant while the temperature increases.

Instead of a stoppered bottle, think of the gas trapped in a cylinder underneath a heavy piston. The pressure is determined by the weight of the piston which is constant. In fact, the pressure must be equal to the weight of the piston divided by the area of the cylinder's cross section. As the temperature increases, the pressure will remain constant, and the piston will rise.