Beta particles are electrons, which carry negative charge.
Charge isn't affected by magnets, unless it's moving. If it's moving, THEN it's electric current, and current feels a force toward or away from magnets.
This question doesn't say whether the beta particles are moving, so we have to assume that they're just laying there, and they don't even know that there's a magnet nearby.
So beta particles will not be affected by either pole of a magnet. (C)
