How many of the following act as electrophiles  ____
i)  $R^{+}$    ii)  $B{r}^{+}$  iii)  $B{F}_3$  iv) $O{H}^{(-)}$   v)  $N{H}_2^{(-)}$     
vi) $S{O}_3$   vii) $Alc{l}_3$   
 

Electron deficient species can act as electrophiles. In SO₃ sulphur atom acts as electron deficient center due to bonded higher electronegative oxygen atoms