My one experience with jury duty was a couple of years ago in Massachusetts.Before being sworn in the judge asked us if there was any reason why we shouldn't be on this jury to try an accused drunk driver.Two or three people,including me,raised their hand.I was called up to the bench and asked by the judge,while several lawyers (presumably prosecution and defense stood nearby),why...and I replied "because my 18 year old niece was killed by a drunk driver (which was true).In unison,every around me...including the judge...said "no,this man cannot serve in this case".
If what I read about jurors in Victoria is correct that seems to be a recipe for biased jurors and unfair verdicts.
My understanding is that they cannot be questioned, but that both the Defence and the Prosecution are allowed to challenge up to three potential jurors each. They can basically only do this based on looking at the jurors and obviously some things (such are religion) are not necessarily visible. If challenged by either, the Juror is not empanneled for that trial. The Prosecution and Defence are allowed to know the Juror's current professions, but that is about it.
Challenges based on gender, race, religion or age are not directly permitted, but as the Prosecution and Defence can see the jurors, and do not have to explain why they challenge, obviously they can form a judgement as to certain things like likely gender, likely, ethnicity, age range, etc.