Answer
a) $Na_2O$
b) $MgO$
c) $FeO$
d) $Al_2O_3$
Work Step by Step
a) $Na_2O$, because $Na_2O+H_2O\rightarrow 2NaOH$
b) $MgO$, because $MgO+H_2O\rightarrow Mg(OH)_2$
c) $FeO$, because $FeO+H_2O\rightarrow Fe(OH)_2$
d) $Al_2O_3$, because $Al_2O_3+3H_2O\rightarrow 2Al(OH)_3$
