It would, but less than the density difference, since you’ve removed weight from the balloon thus gravity has less of a pull on the balloon. My wife (a PE in thermodynamics) was the one that verified that comment before I posted it, hence why I didn’t say it would increase lift by the difference in density.
You could use hydrogen, which is less dense than helium. Then if it catches on fire like the Hindenburg you’d already be in the water.
It wouldn’t help. The thing that gives you lift is the mass of displaced air. Difference from the (lack of) mass of the lifting gas is minimal.
It would, but less than the density difference, since you’ve removed weight from the balloon thus gravity has less of a pull on the balloon. My wife (a PE in thermodynamics) was the one that verified that comment before I posted it, hence why I didn’t say it would increase lift by the difference in density.