Three elements A, B and C have 3,4 and 2 electrons respectively in their outermost shell. Give the group number to which they belong in the modern periodic table. Also, give their valencies.

Explanation

(i) Element A has 3 valence electrons, therefore, its valency is 3 and thus belongs to group `13 (3+10)`. As such it could be any one of the following elements : B, Al, Ga, ln or Tl
(ii) Element B has 4 valence electrons, therefore, its valency is 4 and it belongs to group 14 (4+10). The element B cound be any one of the following : C, Si, Ge, Sn or Pb
(iii) Element C has two valence electrons, therefore, its valency is 2 and it belongs to group 2. The element C could be any one of the following : Be, Mg, Ca, Sr, Ba or Ra.