Ascientist observes the boundary between two tectonic plates for a decade and finds that no new volcanoes have formed over the course of her investigation. does this result support the theory of plate tectonics? why or why not?

This result certainly can still support the theory of plate tectonics. As plates move with respect to one another, there are 3 main ways they can interact at the margins:
1. Subduction zones, where they collide to produce volcanos and ridges
2. Divergent margins, where they are moving away from each other, producing deep sea ridges
3. Transform margins, where the plates are sliding past one another laterally.

Volcanoes are not the only thing associated with plate boundaries. Over a relatively short period of geological time (10 years), and with no volcanic activity observed, it's likely the scientist is observing a divergent or transform margin, as opposed to the subduction margin commonly associated with volcanism.