Heat-induced evaporation without mass transfer

Steps:

• Heating the metal disc to 600°C causes thermal expansion but no mass change.
• Lowering the disc into water transfers heat, boiling some water.
• Boiling produces steam that escapes the beaker as vapor.
• Mass of disc remains constant; water mass decreases due to lost vapor.

Why C is correct:

• Conservation of mass dictates the disc's mass is unchanged (no atoms added/removed); water mass decreases via evaporation, where liquid turns to gas and escapes (phase change law).

Why the others are wrong:

• A: Disc mass does not increase, as no material is added.
• B: Water mass decreases from evaporation, not unchanged.
• D: Water mass decreases due to vapor loss, not increases.

Final answer: C