Answer: The correct pair is, [tex]Fe(OH)_3\text{ and }H_2SO_4[/tex]
Explanation :
(1) [tex]NaNO_3\text{ and }H_2O[/tex]
The balanced chemical reaction will be,
[tex]NaNO_3+H_2O\rightarrow NaOH+HNO_3[/tex]
(2) [tex]Mg_3(PO_4)_2\text{ and }Al_2O_3[/tex]
The balanced chemical reaction will be,
[tex]Mg_3(PO_4)_2+Al_2O_3\rightarrow 2AlPO_4+3MgO[/tex]
(3) [tex]Fe(OH)_3\text{ and }H_2SO_4[/tex]
The balanced chemical reaction will be,
[tex]2Fe(OH)_3+3H_2SO_4\rightarrow Fe_2(SO_4)_3+6H_2O[/tex]
(4) [tex]Li_2O\text{ and }Ba(OH)_2[/tex]
The balanced chemical reaction will be,
[tex]Li_2O+Ba(OH)_2\rightarrow 2LiOH+BaO[/tex]
Hence, the pairs of reactants react together to produce water as one of the product will be, [tex]Fe(OH)_3\text{ and }H_2SO_4[/tex]