What happens to the gas in a cylinder when it is heated?

When a gas in a cylinder is heated, the molecules within the gas gain kinetic energy, leading to increased movement and collision among them. This increase in molecular activity results in the gas expanding, which can subsequently increase the pressure within the cylinder if the volume remains constant.

In scenarios where the gas is not confined (for example, in an open system), the increased pressure can lead to an increase in gas flow. This phenomenon is described by Charles's Law, which states that at constant pressure, the volume of a gas is directly proportional to its temperature in Kelvin. Hence, the correct response accurately reflects the principles of gas behavior under heating conditions.

In contrast, the other options do not accurately represent the behavior of gases when heated: condensing a gas would refer to a phase change typically seen in liquids, while evaporating completely generally applies to liquids undergoing a phase transition to gas, not gases. Additionally, stating that the gas remains unaffected by temperature changes conflicts with the fundamental behavior of gases, which are very much influenced by thermal conditions.