Question

which electromagnet is the strongest?

Explanation:

The strength of an electromagnet is related to the number of wire coils (turns) around the core. More coils generally mean a stronger electromagnet, assuming the same current and core material. Among the four electromagnets, the third one (from the left) has the most number of wire coils, so it should be the strongest.

Answer:

The third electromagnet (from the left, with the most wire coils around the core)