Hydrogen is the lightest gas then why do we use helium in weather baloons and decorating baloons?

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Helium, which weighs 0.1785 gram per liter, is lighter than air, which can be justified by the fact that a bottle filed with Helium is lighter than a bottle filled with air. Helium is the second element in the periodic table after Hydrogen, having atomic number of 2. Hydrogen is not used for filling balloons as it is highly combustible gas. Helium balloons follow the principles of buoyancy, which is applicable to objects floating in water.