If a person on Earth has a mass of 100 kg. What would their mass be on the moon?
Mass will be 100kg on moon too.
Mass is a intrinsic property of a body that will remain constant. The confusion here is the difference in mass and weight.
Mass is constant property of any environment.
Weight is the changing property. With the changes in environment the weight changes. On earth weight is denoted by the product of mass and gravitational acceleration.
Weight(W) = Mass (m)*gravitational accelaration (g)
Weight is measured in Newtons. But in day today life we omit the gravitational acceleration and we represent weight in terms of mass. That's why we call the weight is 100kg and so on.
If you go to moon weight is the property that changes. It change due to the change in gravitational acceleration on moon. Not the mass.