* Mass is Constant: A 5.0 kg mass will always be 5.0 kg, whether it's on Earth, the Moon, Mercury, or anywhere else in the universe. Mass is a fundamental property of an object and doesn't change based on location.

* Weight Changes: What *does* change is the object's weight. Weight is the force of gravity acting on an object's mass. Since the Moon and Mercury have weaker gravitational fields than Earth, a 5.0 kg mass would weigh less on those celestial bodies.

To summarize:

* Mass: 5.0 kg (same everywhere)

* Weight: Different on Earth, the Moon, and Mercury.

Let me know if you'd like me to calculate the weight of the 5.0 kg mass on the Moon or Mercury!