1. You shouldn't put so much salt in the soup.
- shouldn't V
2. It's dangerous to leave put so much salt in the soup.
- It's adj to V
3. It is very dangerous to play with matches
- dangerous = not safe
4. It's dangerous for your children to play with knives.
- It is adj for sb to V
5. It is unsafe to keep medicine in unlocked cupboards
- It's adj to V