Can I choose Commerce subjects as optional Subject IAS exam as I am from Commerce Background???

Yes you can choose commerce subjects in optional subjects in IAS exams Since you are from Commerce background , you can choose among :-
Commerce and accountancy, Economics, Management, Law, Stastics, since these are the subjects that you have studied in graduation in commerce.

If you are good at commerce subject then it will definitely help you in the preliminary and the main examination. The syllabus of Commerce subject will be roughly similar to that of B.com degree syllabus. It will include accounting, finance, taxation, auditing, cost accounting etc.

List of Optional Subjects in IAS Exam:

Agriculture
Commerce & Accountancy
Chemistry
Civil Engineering
Law
Management
Mathematics
Psychology
Animal Husbandry & Vetinary Science
Anthropology
Botany
Sociology
Statistics
Zoology
Mechanical Engineering
Medical Science
Philosophy
Physics
Political Science & International Relations
Public Administration
Economics
Electrical Engineering
Geography
Geology
Indian History

List of Optional Subjects (Literature) - Main
Assamese
Bengali
Manipuri
Chinese
English
French
German
Gujarati
Nepali
Hindi
Kannada
Kashmiri
Konkani
Marathi
Malayalam
Oriya
Sanskrit
Sindhi
Tamil
Telugu
Urdu
Manipuri
Pali
Persian
Nepali
Oriya
Pali
Persian
Punjabi
Russian
Punjabi
Russian