Question

arrange the elements of second and third period in increasing order of their atomic size

Answer 1

Dear User,
Atomic size decreases on moving from left to right across a period. Therefore, the increasing order of atomic size are :
Second period :
F<O<N<C<B<Be<Li
Third period :
Cl<S<P<Si<Al<Mg<Na

The atoms of zero group elements donot form chemical bonds. Hence, their van der Waal's radii are considered which are always larger than covalent radii of halogens.