What would have likely prevented the Hindenburg explosion?

The choice of using helium instead of hydrogen to fill the Hindenburg dirigible is significant due to the properties of these gases. Hydrogen is highly flammable and was the gas used in the Hindenburg, which led to the catastrophic explosion upon ignition. Helium, on the other hand, is non-flammable and would not have posed the same fire risk.

If the Hindenburg had been filled with helium, it would have substantially reduced the likelihood of the explosion because helium’s inert nature means it doesn't ignite or support combustion. Therefore, the decision to use helium could have provided a safer alternative, preventing the tragedy that occurred.

The other choices do not address the core issue of flammability effectively. Using hydrogen rather than helium would have still resulted in danger, as hydrogen's properties as a combustible gas would remain unchanged. The characteristics of noble gases do not relate directly to the combustion risk involved in this scenario. Lastly, choosing a gas that is lighter than air does not inherently address the risks associated with flammability if that gas is still a combustible substance. Thus, the best preventative measure against the Hindenburg explosion, based on its filling gas, would have been the use of helium.