What mass of h2o is formed when h2 reacts with 384 grams of o2?

Answer is: mass of water is 432 grams.
Chemical reaction: 2H₂ + O₂ → 2H₂O.
m(O₂) = 384 g.
M(O₂) = 2 · 16 g/mol = 32 g/mol, molar mass.
n(O₂) = m(O₂) ÷ M(O₂).
n(O₂) = 384 g ÷ 32 g/mol.
n(O₂) = 12 mol, amount of substance.
From chemical reaction: n(O₂) : n(H₂O) = 1 : 2.
n(H₂O) = 12 mol · 2 = 24 mol.
m(H₂O) = n(H₂O) · M(H₂O).
m(H₂O) = 24 mol · 18 g/mol.
m(H₂O) = 432 g.

The correct answer is a

The mass has escaped into a gas which you can not see so the law stays true.