Hint for the first question:
An argument scheme being valid means that all instances of sentences of this form are valid; if the form is invalid, then not all instances are valid. According to this definition, could it be the case that there exist valid instances of an invalid form?
Hint for the second question:
An argument is valid iff in all structures, either at least of the premises is false or the conclusion is true, and invalid iff there exists at least one structure (a counter model) under which all premises are true but the conclusion is false. If the premises are inconsistent, i.e. true in no possible structure, can there be such a counter model that makes the premises true and the conclusion false?