The correct answer is: c. In the Northern hemisphere, the vertical component of the earth's field points down, and in the southern hemisphere, it points up. So the bacteria are not likely to survive.
Earth's magnetic field is called the geomagnetic field and it is magnetic field from the Earth’s interior out into space. The North geomagnetic pole is actually the South Pole of the Earth's magnetic field, and vice versa. Since the poles have the opposite direction, the magnetotactic bacteria wouldn’t survive.