Statement I : ${\left[\mathrm{Al}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]}^{3+}$ is a stronger acid than ${\left[\mathrm{Mg}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]}^{+2}$

 

Statement II : Size of ${\left[\mathrm{Al}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]}^{3+}$smaller than ${\left[\mathrm{Mg}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]}^{+2}$ and posses more effective nuclear charge.

${\left[\mathrm{Al}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]}^{+3}$is stronger acid than ${\left[\mathrm{Mg}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]}^{+2}$ as ${\left[\mathrm{Al}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]}^{+3}$under goes hydrolysis to yield 

${\left[\mathrm{Al}\left(\mathrm{OH}\right){\left({\mathrm{H}}_2\mathrm{O}\right)}_5\right]}^{+2}$and H₃O⁺. Hydrolysis occurs due to small size of Al⁺³, which polarises the lone pair of H₂O due to which it releases a proton.