Question

Atomic number of a few elements are given below
10, 20, 7, 14
(a) Identify the elements
(b) Identify the Group number of these elements in the Periodic Table
(c) Identify the Periods of these elements in the Periodic Table
(d) What would be the electronic configuration for each of these elements?
(e) Determine the valency of these elements

NCERT Class X
Science - Exemplar Problems

Chapter_Periodic Classification of Elements

Answer 1

atomic number :  10
   1s2  2s2  2p6 :    Neon      Group 18 as number of electrons in the outermost shell = 8 the noble gas config.
   period 2          valency:  0   noble gas..
================
Z = 20
   1s2  2s2  2p6  3s2 3p6   4s2  ::  it is a metal..  Calcium.
     It has  2 valence electrons in the outermost shell.  valency -2..
     period 4..   group = 2 = number of electrons in outer most shell.
   period = 4 as  the outermost shell  is 4.
=================
Z = 7
     1s2  2s2   2p3            it is Nitrogen..  it has valency +5 or -3..    group : 18-3 = 15
     it has 5 valence electrons..    it is a non metal.. it is a gas..
         period 2. as outer most shell is 2.

=============
Z = 14
     1s2  2s2  2p6 3s2  3p2        it is  Silicon...
           valency  4  ... 4 electrons in the outer most shell.
         it is in group  18 - 4 = 14.
         period = 3  as the outermost shell is 3.

Answer 2

Elements — Neon (Ne), Calcium (Ca), Nitrogen (N), Silicon (Si)

Group — 18, 2, 15, 14

Period — 2, 4, 2, 3

Electronic configuration— (2, 8); (2, 8, 8, 2); (2, 5); (2, 8, 4)

Valency — 0, 2, 3, 4

I thing it might help you
thank welcome