Sodium carbonate is mainly produced by the Ammonia Solvay process. This is a widely used chemical process to make sodium carbonate (also called soda ash), which is important in glass making, detergents, and many other industries.

Here’s the simple explanation:
- The Solvay process uses salt (sodium chloride), ammonia, and carbon dioxide to make sodium carbonate.
- Ammonia reacts with salt and carbon dioxide in water, forming sodium bicarbonate which then turns into sodium carbonate after heating.
- This process is efficient and economical, and it replaced older, less efficient methods.

What about the other options?
- Haber process: Used to make ammonia, not sodium carbonate.
- Lead chamber process: Used to produce sulfuric acid.
- Decons process: This is not a common chemical process.

So, the correct answer is the Ammonia Solvay process.

✅ Final answer: Ammonia Solvay process.