Final answer:
The correct verb form to fill in the blank is 'está', which means 'is'
Step-by-step explanation:
The correct verb form to fill in the blank in the sentence is está.
The sentence is saying that normally Pablo is very friendly, but today he is unfriendly.
Since the sentence is talking about Pablo's current state or condition, we need to use the verb form está, which is the third person singular form of the verb estar (to be).
Learn more about Spanish verb forms