Consider the above reaction and identify the missing reagent/chemical.

The correct answer is CaO.

Reaction Analysis:
The chemical reaction shown in the image is:
CH₃CH₂COO^-Na⁺ + NaOH + ? → CH₃CH₃ + Na₂CO₃ (under Heat)
This reaction represents the decarboxylation of sodium propanoate (CH₃CH₂COO^-Na⁺) to produce ethane (CH₃CH₃) and sodium carbonate (Na₂CO₃).

Role of the Missing Reagent:
1. The decarboxylation of sodium salts of carboxylic acids is carried out using soda lime, which is a mixture of sodium hydroxide (NaOH) and calcium oxide (CaO).
2. While sodium hydroxide (NaOH) is the active chemical reagent that reacts to eliminate the carboxyl group, calcium oxide (CaO) is essential to keep the reaction mixture dry (as NaOH is highly hygroscopic) and to facilitate the reaction at high temperatures.
3. Therefore, the missing reagent "?" is calcium oxide (CaO).