i wanted to know if its right to want to gain weight but not mass?

Answer 1

muscle wieghs more than fat but fat takes up more space than muscle. i suggest gaining muscle wieght. if you go to gnc or a store like that they should have muscle weight gaining supplements.

Answer 2

Weight = mass on earth at sea level so you can gain weight without mass by going to somewhere with more gravity or speeding up and that's OK, Yes.