Question

You have seen hydrogen balloons fly up in the air. What can you infer about the density of hydrogen from this?

Answer 1

Hint: A balloon is a lightweight bag that can be filled with helium, hydrogen, nitrous oxide, oxygen, or air and then inflated. Balloons may be filled with smoke, liquid water, granular media (such as sand, flour, or rice) or light sources for specific activities. Modern balloons are made of a variety of materials, including rubber, latex, polychloroprene, or nylon fabric, and come in a variety of colours.

Complete answer:
A lifting gas, also known as a lighter-than-air gas, has a smaller density than standard ambient gases and hence rises above them. Aerostats are essential for creating buoyancy in lighter-than-air aircraft, such as free balloons, moored balloons, and airships. Only some gases that are lighter than air may be used as lifting gases. At normal conditions for temperature and pressure (STP), dry air has a density of around 1.29 g/L (gram per litre) and an average molecular mass of 28.97 g/mol, so lighter than air gases have a density smaller than this.
Hydrogen seems to be the most suitable gas for lifting since it is the lightest existing gas (7 percent the density of air). It is simple to manufacture in vast quantities. Just about 7% of the mass of atmospheric air is made up of hydrogen. It is also much less compact than air. This is why Hydrogen was chosen as the fuel for lighter-than-air ships. That is, before one of the hydrogen-fueled ships blew up. Helium, which has a density of 4 gram and a volume of 22.4 litres, is now used in lighter-than-air aircraft. Hydrogen is twice as thick as oxygen, but it is much less dense and non-explosive.
It's safe to assume that hydrogen has a lower density than oxygen.

Note:
However, hydrogen has a number of drawbacks:
Since hydrogen molecules are so thin, they can readily diffuse through multiple fabrics, including latex, causing the balloon to rapidly deflate. One of the reasons why many hydrogen or helium-filled balloons are made of Mylar/BoPET is because of this.