The author has not mentioned as to presently what he is doing .i.e. whether he is studying in class XI or XII or has already completed the class XII examination. He has also not specifically mentioned as to what subjects were studied by him in class XI/XII though it appears that he has studied science subjects.
Regarding the examinations, there is no examination known as IIT or IIM. For pursuing an engineering degree course , JEE (Main) followed by JEE (Advanced) has to be cleared for securing admission in IITs. The candidates who are not able to get admission in IITs, get admission in other engineering institutions depending upon the score obtained.
Similarly, for admission in IIM, CAT examination is required to pass after graduation. In such cases also, those who are not able to get admission into IIMs may get admission in many other management colleges depending upon the score obtained.
Regarding CA, one can opt for that after 10+2 level on passing Common Proficiency Test (CPT) examination.
All the three options are very competitive in nature and has nothing to do with marks/grade obtained at Xth level.
The competitions are easy for those students who prepare themselves well and tough for those students who are not serious in studies. After all every year a number of students get selected in all such competitive examinations through the dint of their hard work.
Let us encourage each other in sharing knowledge.