I have done 12 with science 54.12% and i want to attend in cat can i do b.com after 12 science

To prepare for CAT VARC, candidates must refer How to Prepare for Verbal Ability and Reading Comprehension for CAT by Arun Sharma and Meenakshi Upadhyay and Word Power Made Easy by Norman Lewis along with Wren & Martin High School English Grammar.

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.