Match the following industrial processes with their principal product, and choose the correct option:
| Column I | Column II |
|---|---|
| (a) Pure nitrogen | (i) Chlorine |
| (b) Haber process | (ii) Sulphuric acid |
| (c) Contact process | (iii) Ammonia |
| (d) Deacon's process | (iv) Sodium/barium azide |