Copper turnings are warmed with a nitrate and concentrated $H X_{2} SO X_{4}$ ; a brown gas is evolved and the solution turns blue. Write the net ionic equation with smallest whole-number coefficients, including water. The sum of all coefficients on both sides is:

Answer: C

The brown gas is

NO X_{2}

Cu + 4 H X^{+} + 2 NO X_{3} X^{-} Cu X^{2 +} + 2 NO X_{2} + 2 H X_{2} O

, balanced in atoms (Cu, N, O, H) and charge (+2 on both sides). The sum is

1 + 4 + 2 + 1 + 2 + 2 = 12

. The value 20 would belong to the

NO

equation

3 Cu + 8 H X^{+} + 2 NO X_{3} X^{-} 3 Cu X^{2 +} + 2 NO + 4 H X_{2} O