Final answer:
The magnetic field must have a component into the page when a positive charge moves to the right and experiences an upward force. This conclusion is based on the right-hand rule for the magnetic field direction relative to current and force on a charge. The correct answer is B.
Step-by-step explanation:
The direction in which a magnetic field must have a component when a positive charge is moving to the right and experiences an upward magnetic force is into the page. This is determined using the right-hand rule: When the thumb points in the direction of the positive charge's velocity (to the right), and the fingers point in the direction of the magnetic force (upward), the palm will face in the direction of the magnetic field, which is into the page (towards the palm).
Applying the right-hand rule to a wire along the y-axis carrying current in the +y-direction and finding the magnetic field at a point on the +x-axis, the thumb should point in the direction of the current, and the fingers will curl. Since the point is on the +x-axis, your curled fingers will be pointing into the page, indicating that the magnetic field direction is into the page at that point.