Dear aspirant,

I'm glad that you wish to give the JEE Mains/Advanced Exam. Fortunately, you can give the exam even though you didn't pass your Class 12 that same year. People even drop a year to prepare for better scores in JEE Examinations. So, yes, you can give the exams with no problem whatsoever. I hope that you pass your exams with flying colours,

Hope this helps!

Good Luck!