Answers

2016-02-23T18:53:46+05:30
The X element which has the atomic number 20 is Calcium and when it reacts with oxygen because oxygen has atomic number 8 .
when they reacts 
             ca+o2 = cao ( it forms quick lime )
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2016-02-23T18:56:23+05:30
the element is calcium i.e. Ca
and
when it reacts with element having atomic number 8 i.e. oxygen (O)
then it forms CaO i.e. calcium oxide


i hope it helps.... 
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