zero in the middle of non-zero numbers is always counted as a sigfig
but if it's the last number.. then it may or may not be counted as sigfig
if it's the first one, it is not a sigfig (e.g 0.0002 --> 1 sigfig)
The basic idea behind the rules is that if zero is merely acting as a place-holder, it isn't counted as significant. The rules rely partially on convention to remove ambiguity, so there really is no substitute for just learning the http://www.swt.edu/slac/math/SigFigur.html [Broken].
As tigger said, (i) is ambiguous as written. See Rule 5 in the link.
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