will there be any problem in placement after mca if I drop after bca for 2 year with out joining any job then take mca college
No there will be no problem. If the panelist ask then you can say that you were exploring the career in more detailed way/ you were learning from the online resources/ you were just taking off due to any other reason which is the truth. But in practicality this will not hamper your selection much because if you have good coding skills you will automatically get selected. So don't worry and pursue the course.
To know more about MCA visit the link below:
https://www.careers360.com/courses/mca-master-of-computer-applications
I hope this answer helps. All the very best for your future endeavors!