Answer:
C, D, B and A.
Explanation:
Electromagnet in option C is strongest because it has an iron core and the largest current as compared to other solenoids, following by D and then B whereas solenoid A is the weakest because of the absence of an iron core and has the smallest current. Solenoid having iron core is the strongest solenoid because the core produces more strong magnetic field as compared to no iron core.
