Final answer:
The magnetic field that causes an electron moving along the x-axis to deflect in the y-direction points in the z-axis direction, as determined by the right-hand rule.
Step-by-step explanation:
If an electron moving in the direction of the x-axis enters a magnetic field and experiences a magnetic deflection in the y-direction, the direction of the magnetic field in this region points in the direction of the z-axis. This is determined by using the right-hand rule for negatively charged particles like electrons. When the fingers of your right hand point in the direction of electron motion (x-axis) and your palm faces toward the direction of the force (y-direction), your thumb will point toward the direction of the magnetic field, which in this case would be out of the page or the z-axis direction.