Science

For pursuing chemistry (H) in DU, the percentage of PCM/ PCB is considered.

Online forms will be available on the DU site. Apply online and wait for the cut-off.

If you want to pursue further studies, you can go for PhD.
If not, you can go in teaching line always. You can apply for an assistant professor in college or lecture in school by clearing entrance exams. You can also try for coaching institutes.
If you interested in civil services you can go for that too.

For physics (H), you must have studied maths till class 12th to take admission in DU.

You can go for Dinesh's or Pradeep's books. They are having very good content and a lot of questions.

Hi Alka,
It is good if you have a first class, the better your percentage, the chances of getting admission is high in good universities. In case you don't manage to get a first class then you should really focus on getting super grades on your Bachelor's degree. But overall, if you are trying or planning to study abroad in near future then strengthen your academic profile as best as you can. Having said that, colleges have different admission requirements, some are more competitive than others. 75% is a widely accepted percentage by the top ones.

No, they consider best of four excluding physical education.