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Which is the lightest gas?
A. Helium
B. Hydrogen
C. Oxygen
D. Nitrogen
Correct Answer Is Option = Hydrogen
Notes / Explanation
The lightest gas of all is hydrogen, which is not only the lightest gas but also the lightest of all the chemical elements. Hydrogen is a gas that has no colour, no smell and no taste, and its most notable physical property is that it is extremely light, being far lighter than the ordinary air, which is why a balloon or other container filled with hydrogen will rise and float upward in the air. Hydrogen is also the simplest of all the elements in its structure, and it is by far the most abundant element in the universe as a whole, making up the greater part of the matter in the stars, including the Sun, where it serves as the fuel for the processes that make the stars shine and give out their light and heat. On the Earth, hydrogen is not usually found on its own as a free gas, but it is present in very large quantities in combination with other elements, most importantly in water, which is a compound formed from hydrogen and oxygen, and it is also found in the many substances that make up living things and fuels. Because it is so light, hydrogen was used in the past to fill balloons and large airships, but this use was found to be dangerous, because hydrogen is highly flammable and can catch fire or explode very easily when mixed with air, and after some serious accidents it was largely replaced for this purpose by a heavier but safer gas that does not burn. The flammable nature of hydrogen, however, also makes it valuable as a fuel, and it is used as a source of energy in various applications, with great interest in its potential as a clean fuel for the future, because when it burns it combines with oxygen to form water, without producing the harmful gases that come from burning other fuels. Hydrogen has many other important uses in industry and chemistry. The study of hydrogen and its properties is an important part of chemistry. For PPSC and other competitive examinations, the key points to remember are that the lightest gas, and the lightest of all elements, is hydrogen, that it is a colourless, odourless gas much lighter than air, that it is the most abundant element in the universe and the fuel of the stars, and that it is highly flammable, which makes it dangerous but also useful as a clean-burning fuel.
