Why State Board needs SSN?

It is also to ensure that you don't have any outstanding child support debts, that any US student loans are not in default and that you are not in default of income taxes. Your social security number can also be used to ensure you are not in any database that would prohibit you from practicing as a nurse (such as previous patient abuse).

OP, first of all welcome to the U.S. :) And secondly, get used to being asked for your SSN..you'll be asked for it for basically everything: Job applications, school applications, driver license(i think? its been a while), lease applications...