Electrophiles are electron seeking species. Which of the following groups contain only electrophiles?

1.  BF3,NH3,H2O

2.  AlCl3,SO3,NO2+

3.  NO2+.CH3+,CH3-C+=O

4.  C2H5-,C2H5,C2H5+


(b, c)
All AlCl3, SO3 (Lewis acids), NO2+.CH3+,CH3-C+=O are electron deficient species.
Hence, these are electrophiles.