Difference between Oxidation state and covalency.
Oxidation state is the number electrons a particular atom can donate or accept with favourable change in electronic configuration and minimal energy increase (or maximum lowering of energy).
Covalency is the maximum number of bonds that it can form using its empty orbitals, mostly p, d and f-orbitals by sharing or accepting electrons.
In the given complex aluminium is bonded to one water molecuke and one chlorine, so the covalency is 2. However, the oxidation state of Al is +3.
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