Answers

2016-03-03T19:17:21+05:30
Reasons....
1.the are very inert(inactive)
2.They are present in extremely low concentrations in our environment.
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2016-03-03T22:31:37+05:30
Reason are
1. they were not react with other gas
2. The valance electron in noble gas is 8 so it is full
3. they were not react to other gas because every atom want to full his valance shell with 8 and this is full in his shell
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