Civil Servant (IAS/PCS) exams

It does not matter much. The minimum eligibility for taking up the Civil Service examination is a pass percentage in graduation.
So, the message is loud and clear from UPSC's side that 'It does not matter to me who you were, what matters is only who you are and who you are going to be.'
See there might be 100 reasons for anyone to be scoring low in their school and college years. It might be economic, social or personal reasons. But I sincerely feel that this shouldn't weigh a person down in his UPSC preparation.

About general knowledge, your language which you choose for exam and all the topics of your preferred subject from which you are appearing for exam.

You should choose a subject which you feel comfortable with. Graduating from Zoology, chemistry and computer application can be an advantage. If you have studied these subjects well, you could also opt for one of these subjects as they are included in the syllabus of the UPSC exams. However there are 9 papers you need to appear for, and you have many choices to choose from. Good Luck!!

You need a Bachelor's degree in order to write civil exams. Complete your Bachelor's degree and then apply for civil exams.

As per records and availability of facilities Delhi is perceived as the best city for cracking Civil Services examination conducted by UPSC.

I believe that a person is eligible to appear for CS if he/she qualifies the eligibility criteria.
I hope this would suffice. All the best and god bless you.

Whether Political Science and International Relations is a good optional subject or not depends on your interests and capabilities. Many students who do not have a backgrounf in the subject opt for PSIR optional and qualify UPSC CSE Mains exam with really good marks. 

You have to study each and every field/subject, you have ever faced in your life.
Subjects which you need to prepare for the exam are as follows:-
history, geography, civics, economics, ethics, maths, English, Hindi, Sanskrit, environment science, sociology (as an optional), reasoning, science, current affairs, GK, etc.

Hello Muhammad,
I am very glad to see an aspiring IAS student. After intermediate, you should puruse a Bachelor's degree in public administration, political science or history. History is preferable because it will help you to crack the exam easily. You need to keep yourself updated by reading newspapers and make a note of current affairs. I'll suggest you to join a reputed IAS academy because it will show you an easy map to your goal.
All the best.
God bless you.