A persons weight changes as he travels from earth to space but his mass remains the same
The answer is motion, this is what I would go with because when you are dealing with gases it puts motion in the term of particles.
The difference between an organ and a tissue is that basically tissues are a group of similar cells that works together. Then a group of tissue that works together would make up an organ. Groups of organ working together later makes up an organ system. This is the main difference between an organ and a tissue.
Nickel is a pure substance
Rust is also a pure substance
