Eligibility for NIOS 10th

Secondary Course

This Course is equivalent to the Xth standard. You can choose subjects from the Scheme of Studies given in Table-. However, you will be required to successfully complete a minimum of five subjects, which is compulsory for certification.

Requirement: Minimum Educational Qualification
  • Secondary Course: Certificate of Class VIII passed, or Self Certificate
above taken from this link on NIOS site

Further the official NIOS FAQ handbook  says

What is the eligibility criteria for admission to Secondary Course?
Ans: A person who has passed class VIII and has valid proof of attaining 14
years of age can apply for registration to a Secondary Course.
A self certificate “I have studied enough to be able to pursue Secondary course”
is also eligible for admission to the Secondary course

Also Spoke to Dhruv (who has given 10 and 12 via NIOS - he says "I did not need to prove anysuch requirement when filling up my apllication".