AIIMS 2017 Chemistry Question Paper for free online practice with solutions

According to Fajan's rule :
Covalent character ∝

1

size‌of‌cation

        ∝size‌of‌cation
Among the given species order of size of cations
N3+<O2+<Pb2+<Ba2+
order of size of anions O2−>Cl−
Hence the order of covalent character is
NCl3>Cl2O>PbCl2>BaCl2
BaCl2 is least covalent in nature.