For the complete reduction of copper (II) oxide, 13.44 liters of ammonia were consumed. The mass of copper formed is

3CuO + 2NH3 = 3Cu + N2 + 3H2O
3n (NH3) = 2n (Cu)
3V (NH3) / 22.4 = 2m (Cu) / M (Cu)
m (Cu) = 3 * 13.44 * 64 / (2 * 22.4) = 57.6 g

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