$A$ solenoid is connected to a battery so that a steady current flows through it. If an iron core is inserted into the solenoid, will the current increase or decrease? Explain.

(B) When an iron core is inserted into the solenoid, the magnetic permeability of the core increases significantly compared to air.
This leads to an increase in the magnetic field $(B)$ and consequently the magnetic flux $(\Phi)$ linked with the solenoid.
According to Lenz's law, the induced electromotive force $(emf)$ will oppose this change in magnetic flux.
To oppose the increase in magnetic flux, the solenoid induces a back $emf$ that acts against the battery voltage.
As a result, the net current flowing through the solenoid decreases.