Is this a government secret clearance? If so, you can bet they will find out about it. Even if they were misdemeanors and dismissed, the arrest record is seperate.
Answer the question EXACTLY as it asks. If it asks were you ever arrested..say yes.
If it asks if you were convicted of a felony..say no.
Were you convicted of a marijuana possession or just a recreational user?
Just don't lie, that will really hurt any chance.

