A stationary body is acted upon by a number of forces. State condition which must be applied if it doesn't rotate

the part of the wave he is travelling on is the crest

the answer is the first electromagnet (a). this is because it has more coils around the ferromagnetic material. increasing the number of coils increases the surface area in which the metal interacts with the current in the coil. this enables more atoms in the metal to become aligned hence becoming more magnetized.