Assuming, I apply for voluntary registration and obtain GST registration:When shall I start charging tax i.e. from the date I apply for registration or only after I have got my registration number

1. Only from date the registration has been granted.
2. The tax invoice also can be issued from that date only.
3.  Prior to it neither you can issue tax invoice nor charge any tax on the
   invoice.

(FAQ 9(v)(c): FOOD PROCESSING)