A coil and a bulb are connected in series with a de source. When a soft iron piece is inserted in the coil. Then after some time,

Intensity of the bulb remains the same

The correct answer is Option (1) → Intensity of the bulb remains the same

When the soft iron piece is inserted, the inductance of the coil decrease because the permeability of the iron enhances the magnetic field inside the coil.

This opposes the change in current and hence current through the circuit decreases temporarily.

After the transient phase, the current stabilizes and the bulb's brightness returns to its originality.