\(n_{Al_2\left(SO_4\right)_3}=\dfrac{51,3}{342}=0,15\left(mol\right)\\ PTHH:Al_2O_3+3H_2SO_4\rightarrow Al_2\left(SO_4\right)_3+3H_2O\\ n_{Al_2O_3}=n_{Al_2\left(SO_4\right)_3}=0,15\left(mol\right)\\ n_{H_2SO_4}=3n_{Al_2\left(SO_4\right)_3}=3\cdot0,15=0,45\left(mol\right)\\ m_{Al_2O_3}=0,15\cdot102=15,3\left(g\right)\\ V_{\text{dd }H_2SO_4\text{ }2M}=\dfrac{0,45}{2}=0,225\left(l\right)=225\left(ml\right)\)