The correct order of the size of C, N,P  and S is

C and N are of 2nd period element. Size decreases from C to N.Therefore, size of N < C.P and S are of 3rd period elements. But size of p > S [opposite to the expected trend, i.e. size of S > P].Because P has half-filled stable configuration.Increase of one electron in S causes repulsion between paired electrons 3s2 3px2 3py1 3pz1 and thus size of s is slightly increases from P to S.Moreover, size of 3rd period elements is greater than that of 2nd period.Hence the correct order of sizes isP>S3 rd period >C>N2 nd period