I have sometimes seen the prerequisite for first year courses listed as 60% in <course> 12 or equivalent. I could see that being up to 70% in some cases. More often you just need the credit.
Glancing at
U of T's calendar, some of the upper year courses list specific marks in their prerequisites but they don't list any minimums for the high school courses.
If you've gotten below 70% in Chem 12 I would question why you want to take it as an elective though ;)
Remember that it often takes just as long to do a search or two on Google to try and find the answer to your question as it takes to type it in a post here, let alone the time waiting for a reply.
If your question is "What mark does it take to get into University X", or "What are the requirements to get into University X", it's on their website and/or
electronicinfo.ca (for Ontario schools). Particularly for Ontario schools, those ranges are a pretty good picture of what kind of mark will get you into the program, and if you're more than a couple percent higher it's practically guaranteed unless it requires a supplementary form.
