Consider the following equilibrium. 2 SO2 (g) O2 (g) 2 SO3 (g) The equilibrium cannot be established when __________ is/are placed in a 1.0-L container. A) 0.75 mol SO2 (g) B) 0.25 mol of SO2 (g) and 0.25 mol of SO3 (g) C) 1.0 mol SO3 (g) D) 0.50 mol O2 (g) and 0.50 mol SO3 (g) E) 0.25 mol SO2 (g) and 0.25 mol O2 (g)

From the given reaction we conclude that, the equilibrium cannot be established when there is only one reactant's amount present that means the amount of both the reactants are necessary for the formation of product.

As per question,

(A) 0.75 mol [tex]SO_2(g)[/tex]

The equilibrium cannot be established because [tex]SO_2(g)[/tex] needs [tex]O_2(g)[/tex] to form [tex]SO_3(g)[/tex].

(B) 0.25 mol of [tex]SO_2(g)[/tex] and 0.25 mol of [tex]SO_3(g)[/tex]

The equilibrium can be established because [tex]SO_3(g)[/tex] can decompose to form [tex]O_2(g)[/tex].

(C) 1.0 mol [tex]SO_3(g)[/tex]

The equilibrium can be established because [tex]SO_3(g)[/tex] can decompose to form [tex]O_2(g)[/tex] and [tex]SO_2(g)[/tex].

(D) 0.50 mol [tex]O_2(g)[/tex] and 0.50 mol [tex]SO_3(g)[/tex]

The equilibrium can be established because [tex]SO_3(g)[/tex] can decompose to form [tex]SO_2(g)[/tex].

(E) 0.25 mol [tex]SO_2(g)[/tex] and 0.25 mol [tex]O_2(g)[/tex]

The equilibrium can be established because [tex]O_2(g)[/tex] and [tex]SO_2(g)[/tex] can react to form [tex]SO_3(g)[/tex].

Hence, the correct option is (A) 0.75 mol [tex]SO_2(g)[/tex]