Effects of re-appearing for RBSE Class 12th exams

There are two ways of clearing the said examination. The first way would to appear in your Chemistry Theory Paper coupled with its practical and clear this subject in the compartmental mode otherwise you might all the papers along with your failed ones with a view to clear the examination at one go.
However, there is a catch in it. Keep this thing in mind your latest scorings in all the papers would be treated valid. In case, you have scored more marks in a subject in the previous examination, you would be deprived of such benefits.
Here in your case, Improvement Mode is not applicable to you since you have in one of papers( Chemistry).Had you passed all the papers and were not satisfied with the scorings, you could have appeared in all the papers for the improvement of marks and in that case, your latest scorings would have been taken account.

Yes. You can appear for all the subjects by cancelling the present result. If you cancel the present results whatever marks you scored will not have any relevance. You can appear in all the subjects including the failed ones and you will be given rank also and you will become eligible for all admissions and scholarships also,
Another way is to immediately attend only chemistry and get qualified in the examination. This will be a compartmental pass. Then you can apply for improvement and appear for all the examinations and you can select the best one among the two results.
You have to take a chance based on your confidence and do whichever appears better to you. If I were you I go for the cancellation of the present result and attend all the examinations at once.

If you are confident that you can do well in the improvement examinations then only go for the improvement examinations as if you cancel your present result then your present scores will not be valid and they would not be considered further. In general there is no problem in appearing for the improvement examinations. Other way is that, you can prepare well Chemistry and then give compartment examination. In that case your present scores in the other subjects remain same and you have chance to do well in Chemistry.

As mentioned above, you have failed in chemistry theory paper and didn't get good marks in other subject. So, it is better to reappear in all subject so that you would become eligible for further admission and scholarship. Another way is as, you appear for that subject in which you got failed. For that, you will have to give compartmental exam. In that case, your chemistry marks will change and other subject marks remain same. Then only, you can apply for improvement. And you would be eligible to apply for all examination.

You have mentioned that you had failed in Chemistry subject and you are also not happy with your performance in other subjects. In such a case the better course of action would be that you appear in the main examination next year and as you have one full year to prepare there is enough time for you to do a good preparation and have a good score that time. If you work hard during the year then with your background knowledge of the subjects you can improve yourself to good heights. So I would recommend for going for all the subjects next year and achieve a good scoring.
Please note that if you only give compartment/supplementary exam in chemistry and pass it just with the minimal score then your overall score would be poor and it will not be feasible for you to get an admission in some good UG course. So only alternative is to work hard and achieve good marks next time. If you work hard then there is an added advantage coming to you in natural ways and that is that you can appear for competitive examinations also. Please note that the hard work you do at any stage in your life is not for the immediate gains but helps you in a longer term and if you can visualise, understand, and follow this doctrine in your life you would be a winner.