Here are the correct forms of the words in brackets:

1. **enjoyment**
(Mike's hobby is listening to music. He gets a lot of **enjoyment** from listening to music.)

2. **collecting**
(John is a stamp collector. He has a lot of rare and valuable stamps.)

3. **obesity**
(One third of children in the U.S. is **obese** or **obesity**.)

4. **Outdoor**
(Outdoor activities such as cycling, hiking, and mountain climbing can help improve your health.)

5. **health**
(We shouldn't eat too much junk food for our **health**.)

6. **volunteer**
(They used to **volunteer** to the Salvation Army for donating goods.)

7. **responsibility**
(We need to take **responsibility** for looking after our own health.)