Consider the following reaction is carried out at constant volume:
CaCO_3(s) ⇌ CaO_(s) + CO_2(g)
An equilibrium state can be achieved if one of these conditions are met:

• A. The reaction vessel initially contains CaCO₃ only.
• B. The reaction vessel initially contains CaO and CO₂.
• C. The reaction vessel initially contains CaCO₃ and CO₂.
• D. The reaction vessel initially contains CaCO₃ and CaO.
• E. The reaction vessel contains all three substances.
• F. The equilibrium state can be achieved with any of these combinations.

Answer: (F)