is the adverbial use of the な-Adjective 確（たし）か, meaning ‘to be certain’, or ‘to be assured’. It may be used in the same way as ‘certainly’ or ‘surely’ in English, especially when the speaker wants to highlight (A) is definitely the case.
He is certainly handsome, but he has bad manners.
What I said earlier was certainly out of line. I’m sorry.
Caution - 確（たし）かに
as ‘certainly’ is only used for verifying information, and does not carry the nuance of giving permission, as it does in English.
This is certainly difficult. I underestimated it.
Certainly! You may play video games if you finish your homework.
Caution - When the に is removed, 確（たし）か is often used in a similar way to ‘if I remember correctly’, ‘if I’m not mistaken’, or ‘now that you mention it’.
If I recall correctly,I feel like that person is Takuya-kun’s father.
By the way, how much money did I borrow the other day? If I remember correctly, it was 3 thousand yen, correct?