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The Brainliest Answer!
2015-09-06T14:41:48+05:30
 It is easy . 
Firstly take its atomic number for example Copper ( Cu)= 29
 So its electronic configuration will be:-
           Cu = (2,8,8,8,3)
Therefore as it has 3 in its last orbit it has valency 3.
1 5 1
hmmm
valency of zinc will be:- 2,8,8,12 and its valency is not 12
but if we consider iron then as per you it will be 2,8,8,8
but it isn't noble gas
yes