why does compass become inactive when taken to poles?

Answer 1

Because the magnetic field is pointed vertically at the (magnetic) north pole. That means torque about vertical axis of the compass is zero.

However, it you made a special compass with a needle that could spin freely about its axis regardless of orientation (that is, it did not depend on gravity to balance), and you held it sideways, the needle would point down.

Answer 2

The Earth's magnetic north pole does not line up with the rotational North pole. The magnetic north is actually about a hundred miles or so SOUTH of the north pole (on some island in Canada). The Earth's magnetic south is actually in the antarctic ocean somewhere.

Answer 3

if in the north pole,there in nothing north of north now is there?if in the south pole north pole is 180º north of the point hence will be vertically downwards.