Dear Student,
The answers are:

1. It is easy to be confident if you are well prepared.

2. It was good to see him so happy.

3. You seem to be much slimmer now.

4. Solving this problem is quite tough.

5. It was foolish to talk about his plans so early.

6. For you to commit such a mistake is unbelievable.

7. That you did not like the film is amazing.

8. I am not sure why I must wear a white dress.

9. It is necessary that you reach home before dark.

10. It is very important for us to drink a lot of water.

Hope this helps.

Regards