please tell me scope of 3 year diploma of accounts and auditing from polytechnic and its higher studies.

Diploma courses are after 10th standard. Aim of the course is to develop specialized skills in the selected area (say accounts and audit) in your case. It will be better than 10+2 but lower than B.Com which is done after 10+2 or HSC. Nowdays in industry Graduation i.e. BCom or any other Bachelor deg

Instead of wasting 3 years in getting dimploma in accounts and auditing, why don't you try for a prestigious and lucrative career of Chartered Accountant with the Institute of Chartered Accountant of India? For detailed guideance you can see the Institute's document on Requirements for becoming a C

I dont think there is any provision of doing B.com second year after getting diploma.