Can a unique No. be filled out on a form?

2. Pre-form on the basis, a unique no. filled out on the form

You can add the Unique ID widget in your form, which increases the number by an increment for every submission received.

The below guides will help you out:

https://www.jotform.com/help/79-How-to-Add-Custom-Unique-IDs-to-your-Form-Submissions 

https://www.jotform.com/help/252-How-to-Add-a-Widget-to-Your-Form