Question 6: An electron does not suffer any deflection while passing through a region. Are you sure that there is no magnetic field?

No, we cannot say for sure if the magnetic field exists when the charged particle moves straight in the region.

When a charged particle moves in a magnetic field it experiences a force given by the equation;

Different situation can be possible for a charged particle moving straight in a region of space.

1. There is no magnetic field in the region.
2. There is a magnetic field such that the direction of motion of the charged particle and the magnetic field are same. In such a case the angle θ = 0°. Since sin 0° = 0, therefore, the magnetic force on the charged particle would be zero and the particle would be moving in a straight line.
3. If there is an electric field adjusted such that its force equals to the magnetic field force but having opposite direction. In such a case both force will be cancelling each other.

So it is not possible to say with certainty that no magnetic field exists in the region.