Serio would be the correct answer because Pablo (noun) is a male, and this sentence is singular. Now for a female the correct adjective would be seria. Remember all nouns have a gender whether it be a place, or thing.
Answer:
1. es
2. es
3. somos
4. son
5. soy
6. estoy
7. estamos
8. esta
9. estan
10.esta
Explanation:
Ser and estar forms
you got it right