Which formula equation shows a reversible reaction?"
A) 2Na + F₂ → 2 NaF
B) CaCO₃ → CaO + CO₂
C) NH4Cl(s) ↔ NH₃(g) + HCl(g)
D) 2H₂O₂(aq) → 2H₂O(l) + O₂(g)