The correct answer would be option B. This is because there is 1500g of gas inside of the balloon so if all of the gas escaped then its mass would decrease by 1500g. It couldn't have decreased by less than 1500g because then that would have to mean that all of the gas didn't escape, which it did. If it decreased by more than 1500g then there would have had to be more than 1500g of gas in the balloon to begin with. This is why the answer would be B. 1500g.
