CBSE 12th

Yes, you should register for private institution, then you can appear for the exam privately.

After improvement exam you have to show the improved marksheet as it is valid now.

No, it is not available.
Jadavpur University B.Sc Course Details
It is a three-year full-time course divided into 6 semesters. The institute provides B.Sc degree across five specializations:
Physics
Chemistry
Mathematics
Geological Sciences
Geography
Jadavpur University B.Sc Admission Guidelines:
Applicants will be required to appear for the admission test conducted by the university.
After declaration of the result, a merit list will be released by the university for further selection.
On the basis of the merit list, selected candidates are called for the interview for final admission.

You are eligible for BBA and B.Com (Hons) for good college in Ahmedabad and please apply soon to college near you, You are late for now because once you get you results, the immediate action to be taken is apply for as many college as possible irrespective of your marks. College work on first come first serve basis.

B.Sc. Is an honours degree, BCA is a Bachelor of computer application degree software based and B tech is engineering degree so always B.Tech is the best but BCA is not bad at all.

Dear Candidate, Indian Institutes of Information Technology (IIITs) are a group of 25 interdisciplinary technology-based engineering research institutions focused on information technology. Admission to the four-year B.Tech. Programme is granted by the Central Seat Allocation Board 2021 based on JEE Main merit. Earlier, there used to be a compulsory 75% in the 12th criteria, which was temporarily removed for admission to IIIT for the years 2020 and 2021 due to the COVID pandemic situation. As of now, the criteria is still relaxed for the current session; however, it might get restored in the future. I hope this helps.

NTA has removed the 75% criteria from the minimum eligibility norms as per the recent JEE Main. 2022 notification, available on JEE Main.
However, for B.Arch it is necessary to have at least 50% in Physics, Chemistry and mathematics as well as 50% aggregate in qualifying examination. Top 2,50,000 successful candidates on the basis of JEE Main 2022 exam will be eligible to attempt the JEE Advanced exam. And for IITs and NITs the 75% criteria is not removed, either candidate must have 75%in 12th or they must be in the top 20 percentile in their class 12th exam (65% for SC/ST candidates). .

As of now all the central universities Admission is going on the basis of CUCET score and good private university also take Entrance exam before Admission so
First take the Entrance test and score eligible marks for Admission, so you can get admission college. Just you must have 51% approximately in 12th to get admission.

As all Central University started taking Admission through the CUCET, your 12th marks doesn't matter to get admission in B.A. Psychology or any other stream. You can take entrance exam and score eligible marks so you can get Admission in DU.

Most of the top College take admission on Entrance Basis or Merit basis. Students should have passed out 12th (10+2) with not less than 51% marks to be eligible for Entrance (the percentage may vary from college to college).