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   hy·dro·gen/?h?dr?j?n/

   
   
    
   
   
   
   

   Noun: A colorless, odorless, highly flammable gas, the chemical element of atomic number 1.  More »

   
   

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It is an element.  It is a natural resourse.  It cannot be broken down into other things.  It is the first element on the periodic table meaning it is the lightest one. 

Hydrogen is the naturally occuring gas whose atomic number is 1 and & listed in top most of the Group IA in the Modern Periodic Table.

It is also the lightest gas known.

Hydrogen is the lightest of the chemical elements and has the simplest atomic structure, a single electron orbiting a nucleus consisting of a single proton. It is by far the commonest element in the universe, although not on the earth, where it occurs chiefly combined with oxygen as water.