When the force of gravity is smaller than the force exerted by the magnet, it will fall. That will depend on the distance from the magnet, the strength of the magnet, and the percentage iron content. (100% iron coins will rust and disintegrate pretty quickly, I think, so I don't think you can get coins out of them.)
Because light is scattered by particles or groups of particles the same size as their wavelength. Most of the particles in the atmosphere are either smaller than visible light's wavelength, or only just big enough. This means only the smaller wavelengths have any scattering, i.e. blue and purple. This scattering across the sky makes the sky look blue. The reason the sky doesn't look purple is because there is less purple in sunlight and we find it harder to see than blue. This explains other effects too. The reason the sun looks yellow is because the blue light is scattered out of the direct sunlight across the sky leaving a shift in the average colour of the sunlight. This effect is especially pronounced when the sunlight has to go through a long distance of atmosphere, e.g. at sunsets. This means only the longest wavelengths can get through i.e. red and orange light. You can see the same effect with silica aerosol, too.