Hii,

The required percentage for a B.Com seat varies by college.  In general, you must get at least 50% on your 12th grade tests from a recognized board.  Top colleges, such as Delhi University, may ask for 90% or more.  Some private universities accept lower grades, about 45%, particularly in restricted categories (SC/ST/OBC).

Many colleges require entrance examinations, such as the CUET, thus your exam score is important.  Check the respective college's website for exact criteria, which varies.