When `N_(2)O_(5)` is heated at certain temperature, it dissociates as `N_(2)O_(5)(g)hArrN_(2)O_(3)(g)+O_(2)(g),K_(c)=2.5` At the same time `N_(2)O_(3)` also decomposes as :
`N_(2)O_(3)(g)hArrN_(2)O(g)+O_(2)(g).` "If initially" `4.0` moles of `N_(2)O_(5)` "are taken in" `1.0` litre flask and alowed to dissociate. Concentration of `O_(2)` at equilibrium is `2.5` M. "Equilibrium concentratio of " `N_(2)O_(5)` is :