Is P/poly known to be in RE? If yes what other classes is it known to be part of.
$P/poly$ is NOT a subset of $RE$. Specifically, the unary non-halting problem (i.e. given a Turing Machine encoded in unary, does it run forever?) is in $P/poly$ but not $RE$. In fact, every undecidable unary language is in $P/poly$.