Question

Since 1917, all puerto ricans have been considered u.s. citizens, but they are not represented in congress and cannot cast ballots in presidential elections. in this sense they are:

Answer 1

In this sense they are "disenfranchised".

To disenfranchise someone means to strip them of a right which was legally their's, or to deprive a privilege or immunity from someone. This is specially when right to vote is taken away from an individual like the Puerto Ricans have been treated since 1917.