Oxidation state and covalency of Al in [AlCl(H₂O)₅]²⁺ are

Given, 

$$\begin{gathered} [\mathrm{AlCl}{\left({\mathrm{H}}_2\mathrm{O}\right)}_5{]}^{2+} \\ \mathrm{x}+(-1)+5(0)=+2 \\ \mathrm{oxidation} \mathrm{state} \mathrm{of} \text{'}\mathrm{Al}\text{'} \left(\mathrm{x}\right)=+3 \end{gathered}$$

We know, covalency is the number of molecules or atom or ion attached to particular atom. For this complex, we can see that aluminium atom is attached to one chloride ion and five water molecules. So, total six molecules or ion are attached to the aluminium atom. This tells us that the covalency of aluminium in $[\mathrm{AlCl}{\left({\mathrm{H}}_2\mathrm{O}\right)}_5{]}^{2+}$ is 6.