Hydrogen

Things to remember

• The thick layer of air which surrounds the earth is called atmosphere.
• Hydrogen is the lightest gas, so it is found only in combined state and not in air.
• Hydrogen gas can be obtained from the action of metals with acids, alkalis and water.
• Hydrogen is combustible gas but not a supporter of combustion.
• A catalyst is as a chemical substance which alters the rate of chemical reaction, itself remaining chemically unchanged because it does not take part in chemical reaction.