Hello Aspirant!

To be eligible for appearing in most of the competitive (mainly entrance) exams after 12th, you just need to have minimum 60% marks as your aggregate (P+C+M) and pass individually in all your core subjects.

Having 60+ marks individually in all the 3 subjects however keeps you on the safer side and definitely enhances your percentage, which can help you in merit-based tie breaker situations and selection/opportunities (like availing scholarships) on the basis of merit (aggregate).

Hope it helps.
Don't hesitate to ask in case of further queries.