False A premise may be true without being known to be true. It is impossible for the conclusion of a valid argument to be false. If the premises of the argument are false, the conclusion may also be false. An ambiguous word can mean two different things. True This is the definition of ambiguous.
Ambiguous words have two or more different definitions, so they can mean two different things.
Appeal to popularity is the same thing as common knowledge. False Appeal to popularity is a fallacy, common knowledge is a method of judging acceptability. The truth of an a priori statement can not be known without experience. False A priori statements can be known to be true without experience, by definition. Whenever a premise of an argument is implicit, that premise is not relevant to the conclusion of the argument.