Which argument is not valid?

Question

1.) Given: a→b
a
Conclusion: b

2.) Given: a˅b
~b
Conclusion: ~a


3.) Given: a→b
~b
Conclusion: ~a

4.) Given: a→b
b→~c
Conclusion: a→~c

Answer 1

#2 is not an argument, since there is no implication.