I want to load 100 questions to the user browser (About 100 user at once from a single server) and store the options selected by user to the browser until the user click on Final Submit.
The questions will be retrieved using ajax when user is still answering.
I have tried PHP session and retrieved with AJax but I have a feeling that it is not the bet approach.
Is session okay? Or should I tried something else
Local storage is the best way. Since, you're saying 100 questions and then options for each of them. Local storage used to have a limit of 10 MB.But has changed a lot since then. I believe 100 MB is also possible. Although would not advise those kind of numbers in browser.
Please read this to understand how to operate Local storage.
http://tutorial.techaltum.com/local-and-session-storage.html