Question

Give reason: Sulphur is placed in group 16(VI), chlorine group. 17(VIIA) but argon in group 18(0 group) of the periodic table.

Answer 1

The positions of elements on the periodic table is determined by their electronic configurations.
especially elements are placed in particular groups based on their valence electrons.
 
(valence electrons : the electrons in the outermost shell of an atom)
so the electronic configuration of the mentioned elements :
sulphur : (2,8,6)
the no of valence electrons is 6, so it is placed in the 16th group.
chlorine : (2,8,7)
the no of valence electron is 7,so it is placed in 17th group.
Argon : (2,8,8)
the no of valence electron is 8, so it is placed in 18th group.