Which is the best book or resource for CAT VARC?

FIB is not important for CAT VARC as no direct questions are asked. However, it plays a role in VARC preparation and practice.

There are no direct Fill in the Blanks-based questions in CAT exam. Candidates must however practice FIB questions to improve word usage in sentence.

You can refer How to Prepare for Logical Reasoning for the CAT by Arun Sharma and Logical Reasoning and Data Interpretation for the CAT by Nishit K Sinha.

Although syllogism rarely appears in CAT exam, you must not skip it thinking it is not important. Every topic included in CAT syllabus is important.

In the past few years, hardly any direct question has been asked from Syllogism. However, since it is a part of Logical Reasoning, candidates can expect 3-4 set-based questions.