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(a) What do you mean by valence electrons? 

(b) Write the electronic configurations of element K(19) ad N(7). 

(c) Write the number of valence electrons in each of these elements. 

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(a) The number of electrons present in the outermost shell of an atom is known as valence electrons. For e.g., 

the electronic configuration of Na (11) is              K  L  M

                                                                             2  8  1

Thus, the number of valence electrons present in Na is 1.

                                                                     . K L M N 

(b) Electronic configuration of K (19) =          2 8 8 1 

Electronic configuration of N (7) =                 2 5 

(c) No. of valence electrons in K (19) = 1 (as 1 electron is present in last shell) 

No. of valence electrons in N (7) = 5 (as 5 electrons is present in last shell)

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