The balanced equation of the reaction is:
[tex]O_2 + 2 NO[/tex] ⇒ [tex]2 NO_2[/tex]
Every gas occupied 24 L in one mole in r.t.p. according to the equation:
[tex]24 \times n = V[/tex]
8/24=0.333 mol
2 moles of NO makes 2 moles of [tex]NO_2\\[/tex] so
0.333*24=8L