Why don't two magnetic field lines intersect each other?

Consider a circular loop of wire lying in the plane of the table. Let the current pass through the loop clockwise. Apply the right-hand rule to find out the direction of the magnetic field inside and outside the loop.

Choose the correct option.
The magnetic field inside a long straight solenoid-carrying current

1. is zero.
2. decreases as we move towards its end.
3. increases as we move towards its end.
4. is the same at all points.

Which of the following property of a proton can change while it moves freely in a magnetic field? (There may be more than one correct answer.)

1. Mass
2. Speed
3. Velocity
4. Momentum