please help me how i can hack gmail account

What are the options available to hack a gmail account. I lost one password of the oldest account that I was using. I do not remember any security question and now it looks that someone is using the same. I need some way to access that. I reported the same to Google, which replied me to full-fill the security question or verification process to get my account working back again. The issue is that I also do not remember the recovery email I had interlinked with it.

It is illegal. You cannot do that. And if you need that account to be closed you can report to Google. Do not attempt to go for any unethical way to access email accounts. If you are traced you will be landed in jail and also you can get ban to ask such questions here.