Verified Answer :

Molar mass of Al2(SO4)3 = 342.15g/mol


\(7.20gAl2(SO4)3 * \frac{1mol}{342.15g} = .0210434mol\)


\(.0210434molAl2(SO4)3* \frac{12molO}{1mol} = .25252mol O\)


Molar mass of O = 15.9994g/mol

\(.25252molO* \frac{15.9994g}{1mol} = 4.04g O\)