Final answer:
For the chemical formula equation that shows a reversible reaction, an equation with a double arrow is indicative of reversibility. Since the question's options do not show double arrows, we consider common reversible processes, which points to option c) NH4Cl(s) → NH3(g) + HCl(g). The equations provided in the question vary in whether or not they are balanced, with option a being unbalanced and options b and c balanced.
Step-by-step explanation:
The question asks which formula equation illustrates a reversible reaction. A reversible reaction is typically represented by a double arrow in a chemical equation, indicating that the reaction can proceed in both the forward and reverse directions. Since none of the option's provided explicitly show a reversible reaction with a double arrow, we should look for hints of a reaction that can commonly occur in both directions. Option c) NH4Cl(s) → NH3(g) + HCl(g) represents the decomposition of ammonium chloride into ammonia and hydrogen chloride, which is indeed a reversible process in reality although not depicted with double arrows in the options provided.
In terms of equation balancing, let's examine the provided equations:
- a. 2Na(s) + O2(g) → 2Na2O(s) - This equation is not balanced because the oxygen atoms don't have the same count on both sides.
- b. CH4(g) + 2O2(g) → CO2(g) + 2H2O(l) - This equation is properly balanced with equal numbers of each type of atom on both sides.
- c. AgNO3(aq) + 2KCl(aq) → AgCl(s) + KNO3(aq) - This equation is also balanced with all atoms accounted for on both sides.