A colorless crystalline substance upon heating in a test tube, becomes powdery, shows no visible condensations or other changes inside the test tube, and after cooling, the mass of the contents of the

The question describes a colorless crystalline substance that, when heated, becomes powdery, shows no visible condensations or other changes inside the test tube, and decreases in mass after cooling.

Let's analyze the observations:

• Crystals become powdery: This indicates a change in the solid's physical structure, often due to decomposition or loss of a component.
• No condensations or other visible changes inside the test tube: This is crucial. It means no liquid droplets (like condensed water) formed, and no colored gases were produced.
• After cooling, the mass of the contents of the test tube decreases: This definitively means that some substance left the test tube during heating. Since it left, it must have been in a gaseous or