The correct option is It is nearly uniform inside the coil.
Explanation
A solenoid is a long coil of wire wrapped in the form of a helix. When an electric current flows through it, it generates a magnetic field. The nature of this field is determined by the superposition of the magnetic fields generated by each turn of the coil.
Analysis:
For a long, straight current-carrying solenoid, the magnetic field lines inside the coil are parallel to the axis and closely spaced. In physics, parallel and equidistant field lines represent a uniform magnetic field. This implies that the magnetic field strength is approximately the same (uniform) at all points inside the solenoid. The field is strong along the axis but decreases significantly near the ends and is negligible outside the solenoid.
Key Takeaway:
The magnetic field inside a long current-carrying solenoid is uniform, meaning it has a constant magnitude and direction throughout the interior volume.