The question is somewhat completely and utterly wrong. 

A where clause does not evaluate TO anything at all.  In this case there will never be any rows matching the filter (assuming the normal ANSI NULLS setting), so the best answer among all of the possible but all incorrect answers is "False".  "Unknown" is not correct, because it is "known" that no rows will match.

The expression IN the where clause evaluates to Unknown, but that is not what the question asks.