Hello Pugazh Vanan !

The HSC registeration number must be the unique number present in your marksheet. If there is no number present in your marksheet , just enter your roll number then , but there must be a registeration number in your marksheet or admit card. Please check both of them.

Check out the following website for more information:

Https://medicine.careers360.com/articles/tamil-nadu-mbbs-application-form