The compound Fe₄[Fe(CN)₆]₃ is known as Prussian Blue, and it is insoluble in water. On the other hand, compounds like K₄[Co(CO)₆] are soluble due to the ionic nature of the complex.
Thus, the correct answer is (1), as Prussian Blue (Fe₄[Fe(CN)₆]₃) does not dissolve in water.