True enough.
I briefly tried looking up the price for each alloy, but didn’t find anything.
I suppose those two alloys probably have different amounts of their respective impurities, and so one would, in fact, be purer than the other. But amount of total impurity isn’t really the relevant factor, here.
True, but even this fact makes the McDonalds’ solicitation factually wrong.
5182 alloy (top and tab): 95.2% Aluminium
3004 alloy (body): 95.6% to 98.2% Aluminum.
In other words, the cans are the purer form of aluminum. The tops (and tabs) are less pure.