If I delete my Stack Overflow account, will all my questions be deleted which I have asked on SO. Due to privacy I need to delete all my questions, is it possible?
Yes, it is possible.
But, if your account gets deleted the questions and answers will linger on without an associated account. This is to preserve as much information as possible. If you really need to get rid of all your questions and answers, then you need to contact the team and request it. Though, they don't like such requests because it means that you're taking away valuable information from the community forever.
The best way for all of us would be to make your account anonymous and then request to remove the account without removing the questions and answers.