I finished my B.Tech in June'16 after which I worked for 6 months and left job in January'17. How would this be treated as during PI round?

Firstly, there shall be 10month gap in your profile and woukd be required to justify as why you left this job.
Obviously it wont hamper your chances, but if you're mentioning that you have taken long gap for preparing then it is definitely not apt.
All you can mention is you wanted to join volunteeri g work and also gain some technical certificate course and hence required time  to comolete the same.
You need to validate this with relevant authentication certificate to prove that you are not bluffing.
At last you can mention, you were preparing for CAT simultaneously to showcase your interest for the management course.
Hope it clears your doubts and woreies. Keep me oosted incase you have any doubts.

It will be counted as 6 months of work experience and it will not gain you any extra points in your aggregate score which comprises of many factors such as CAT marks, 10th 12th and graduation percentage, work experience etc. with different weightages for different colleges. Generally you get additional marks for more than 1 year, this range also varies from college to college.

If you haven't mentioned about your work experience in your CAT form then let it be skipped but if you have added it in your form make sure in any PI you don't mention about the reason for leaving tahtbyou were not able to do studies along with work becuase while pursuing MBA degree it's gonna be 20 times tougher. If you are gonna mention this as a reason it will show your weakness which will definitely create a negative image in the minds of interviewers and it will hamper your selection.

So try to frame some other like medical problem or something else so that you can skip that question with a benefit of doubt. Also make sure you prepare properly about all you used to work for those 6 months. This will justify your reason and win the trust of interviewers that you had a good knowledge about your work and used to work properly. You left the job with genuine reason and then with the ambition of pursuing MBA degree you start preparing for CAT exam.

All the best!!

Equivalent to 6 months of workex, that is a  zero scope for workex. Don't let this be a point of discussion in PI that You couldn't take on work and studies together as in MBA you are expected to cope up with much more of it.