Question

For the following elements predict the group number and block to which they belong : A(at.no.=9) ,B (at.no.=12),C(at.no.=29) ,D (at.no.=18),E (at.no.=5)

Answer 1

using the atomic number you get the number of electrons it has in it so,
A has 9 electrons which means 2,7 so is a halogen and belongs group-17
B has 12 electrons which means 2,8,2 so is a alkaline earth metal belonging to group-2
C has 29 electrons which means 2,8,18,1 so belongs to transition metals in group number-11
D has 18 electrons which means 2,8,8 so belongs to noble gases(group-18)
E has 5 electrons which means 2,3 so belongs to group-3

hope this helps!