The balanced chemical equation for the reaction of sodium hydroxide (NaOH) with water is:

2 NaOH + H2O → 2 Na+ + 2 OH- + H2O

From the equation, we can see that 2 moles of NaOH react with 1 mole of H2O to produce 1 mole of water. Therefore, the number of moles of water formed is half the number of moles of NaOH reacted.

Number of moles of water formed = (2.75 x 104 mol NaOH) / 2 = 1.375 x 104 mol H2O

Now, we can use the molar mass of water (18.015 g/mol) to convert moles of water to mass.

Mass of water formed = (1.375 x 104 mol H2O) x (18.015 g/mol) = 2.48 x 106 g

Therefore, the mass of water formed when 2.75 x 104 mol NaOH reacts completely is 2.48 x 106 g.