well guys i know the answer now.as ashgirl(my dear sis) just said that elementary reactions take place in one step.therefore the order of reaction and molecularity should be same for these reactions(as my teacher told me).

order of this reaction is 3/2.but molecularity cannot be a fraction and hence this is not an elementary process.

(my teacher has taught for 5 years in FITJEE,so plz don't doubt her answer)