Option 1 -> A current-carrying solenoid generates a magnetic field inside, so it cannot be zero.
Option 2 -> For an ideal long solenoid, the magnetic field inside is uniform and parallel to the axis, given by B = μ₀nI.
Option 3 -> The field doesn't increase towards the ends; it remains constant in the central region and weakens at the edges.
Option 4 -> The field remains uniform throughout the central region, not decreasing continuously toward the ends.
Hence, Option 2: Is uniform inside the solenoid -> In a long straight solenoid, the magnetic field lines are parallel and evenly spaced inside, creating a uniform magnetic field throughout the central region, with magnitude B = μ₀nI (where n is turns per unit length and I is current) -> correct