Here are the word forms to fill in the blanks based on the prompts provided:

1. How many **nations** are there in the UNO? (nation)
2. The **national** anthem of Great Britain is "God Save the Queen." (nation)
3. He says poetry is **interesting**. (interest)
4. It sometimes **interests** his friends in reading aloud some beautiful poems. (interest)
5. He chooses his career as a **mathematician**. (mathematics)
6. He spent his free time on working scientific problems - **mathematical** puzzles. (mathematics)
7. In science, the **choice** is clear-cut. (decide)
8. Winning the race was an **achievement**. (achieve)
9. We are faced with a difficult **choice**. (choose)
10. Our school team won three **successive** games. (succession)
11. You evidence was **decided**. (decide)
12. The United Nations is an international one. (**organization**)
13. The Worker’s Club is a seminar on safety. (**organize**)
14. Workers demand prompt **payment** from their employers. (pay)
15. They lived happily despite their **poverty**. (poor)

Feel free to ask if you need further assistance!