Fill in the blank with the appropriate Phrasal Verb from the options given below :

I thought I would ________ for a cup of Tea. Is that fine?

drop in

The correct answer is drop in.

The phrasal verb drop in means to visit someone casually and unexpectedly. It is the most appropriate verb to use in this context because it suggests that the speaker is not making a formal appointment or arrangement.

The other three options are not as appropriate:

• Drop off means to leave something or someone somewhere.
• Drop  can have a number of meanings, but none of them are relevant to this context.
  
• Drop out means to leave a school or other organization before completing it.

Here is the complete sentence with the phrasal verb:

I thought I would drop in for a cup of tea. Is that fine?