Final answer:
The formula of caustic potash or potassium hydroxide is KOH. The formula of its carbonate is K₂CO₃.
Step-by-step explanation:
The formula of caustic potash or potassium hydroxide is KOH. To determine the formula of its carbonate, we need to consider the reaction between potassium hydroxide and carbon dioxide. When potassium hydroxide reacts with carbon dioxide, it forms potassium carbonate and water. The balanced equation for this reaction is:
KOH + CO₂ -> K₂CO₃ + H₂O
From the balanced equation, we can see that the formula of the carbonate is K₂CO₃. Therefore, the correct answer is option a. K₂CO₃.