In this question, we are considering a sample of carbon dioxide undergoing a transformation from solid to liquid and then to gas. Let`s analyze each option to understand the changes that occur during this transformation:

Option 1: A change in mass - When carbon dioxide undergoes a phase change, such as from solid to liquid or from liquid to gas, there is no change in the total mass of the substance. The number of carbon dioxide molecules remains the same throughout the transformation. Therefore, option 1 is incorrect.

Option 2: A change in density - Density is a measure of how much mass is contained within a given volume. During the transformation of carbon dioxide from solid to liquid and then to gas, the molecules become less densely packed as they move from a solid state to a liquid and then to a gas. This means that the density of the sample of carbon dioxide will change. Therefore, option 2 is correct.

Option 3: A change in composition - The composition of carbon dioxide, which consists of one carbon atom bonded to two oxygen atoms, remains the same during the phase change. The arrangement and nature of the atoms do not change. Therefore, option 3 is incorrect.

Option 4: No change in physical properties - This option is incorrect as there is