Which problem is already balanced? SO_(2)+H_(2)O-gt H_(2)SO_(4) PbO_(2)+2H_(2)-gt H_(2)SO_(4) NaOH+3AgNO_(3)- gt 3AgOH+NaNO_(3) 2Na+2H_(2)O-gt 2NaOH+H_(2)

The balanced chemical equation is:<br /><br />$2Na+2H_{2}O-\gt 2NaOH+H_{2}$<br /><br />In this equation, the number of sodium (Na) atoms, hydrogen (H) atoms, and oxygen (O) atoms are equal on both sides of the equation, indicating that the equation is balanced.