AS Chemitry question past paper problem

[M@35TR0]

14 Aluminium chloride catalyses certain reactions by forming carbocations (carbonium ions) with
chloroalkanes as shown.

RCl + AlCl3 → R+AlCl4

Which property makes this reaction possible?

A) AlCl3 is a covalent molecule.

B) AlCl3 exists as the dimer Al2Cl6 in the vapour.

C) The aluminium atom in AlCl3 has an incomplete octet of electrons.

D) The chlorine atom in RCl has a vacant p orbital.

Answer is C but dont understand y. Can someone help???

 

[gary221]

Draw the arrangement of electrons of AlCl3...like this :
And u will see that thr r only 6 electrons around Al ie incomplete octet...as a result it can accept 1 more Cl atom to complete its octet..
Hope i helped!
P.S. excuse the bad drawing..nt very gud at it..

 

[M@35TR0]

GOt it thanks gary221