Answer
a) No.
b) Yes.
Work Step by Step
$$\color{blue}{\bf [a]}$$
We know that the current flow of positive charges in one direction
through this circuit will give us the same observations and measurements as the flow of negative charges in the opposite direction.
So there is no way to distinguish between them.
$$\color{blue}{\bf [b]}$$
We can use a charged parallel plate capacitor (conductor) to test both hypotheses.
So we need to use glass and plastic rods and rubbing charges onto or off of the plates in discrete amounts.
Then we can connect them to a conducting wire. Then the capacitor will
discharge as charges move through the wire from one plate to the other.
This experiment is proof that the charge is carried as discrete particles