Here are the correct forms of the words for each sentence:

1. Avatar is probably the **worst** film I’ve ever seen! (bad)
2. I think Men in Black 1 was as **exciting** as Men in Black 3. (excite)
3. Dong Ho paintings are made with **natural** colours. (nature)
4. I have a **toothache**, so I must go to the dentist. (tooth)
5. Junk food is **unhealthy**, so we shouldn’t eat too much junk food. (health)
6. **Community** service has a lot of positive effects on students. (serve)
7. **Disabled** people find it difficult to have a job. (disable)
8. I’d like to work as a volunteer for a charity **organisation**. (organise)
9. He made a £5000 **donation** to charity. (donate)
10. The Soup Kitchen is a **non-profit** organization that provides free meals for needy people. (profit)
11. The homeless shelters are entirely staffed by **volunteer** workers. (volunteer)
12. The organization is funded by **charitable** donations. (charity)
13. We help the **elderly** with housework and gardening. (old)

Feel free to ask if you need further assistance!