When someone in C1 grade becomes eligible for Promotion to C2 and how much is the pay hike?

Depends on the manager I think.Can you please tell does C1Y to C1 happens automatically in system after completion of 2 years in organisation (2 year anniversary)or do we have to raise appraisal for it

12-15%

Depends on manager but not less than total 3.5 years exp for C2. Hike percentage 10% generally