Answer the following question given this paragraph: Helium has long been used in balloons and blimps. Since it is much less dense than air, it will float above the ground. We can buy small balloons filled with helium at stores, but large ones (such as the balloon seen above) are much more expensive and take up a lot more helium. Q: What sort of gas is found in balloons and blimps, and is used to make them float in the sky? A:

Pick your answer from:
(i) oxygen.
(ii) hydrogen.
(iii) radon.
(iv) helium.
The answer is:
(iv)