Question

If gas has no weight then why lpg is said to have more weight when full and less weight when empty ?

Answer 1

Even gases have weight but it is very negligible. so we can say it doesn't has any weigh

LPG has compressed gas which means that a large amount of volatile gas is present in cylinder
This compresses gas inside it so much that it become liquid inside lpg.
LPG---Liquid Petroleum Gas
By its full form we can understand it better.
as liquid has more weight so compressed gas in lpg gas has much weight when full