In AlCl₃, ‘Al’ is deficient by 2 electrons to complete the octate or attain noble gas configuration. Electronic configuration of Al is [Ne]¹⁰3s²3p¹, so aluminium has 3 electrons in the outermost shell, when it is bonding with 3 chlorines each shares an electron making a total of 6 electrons so aluminium is still deficient of 2 electron to complete octate(8) hence it act as an electrophile.

SO₃ is bonded with 3 oxygen atoms which are more electronegative than sulphur hence tend to pull the electron density towards themselves(-I effect) leaving a positive charge on sulphur making it act as an electrophile.

Rest all i.e., NO₂⁺ , CH₃⁺ , CH₃ –C⁺ = O are positively charged, hence electron deficient and act as electrophiles.