A block of iron can easily float in which of the following liquids?

• Objects having a density less than that of the liquid in which they are immersed, float on the surface of the liquid. 
• Whereas if the density of the object is more than the density of the liquid in which it is immersed then it sinks into the liquid.
• The density of iron is 7.874 g/cm³ which is less than the density of mercury which is 13.6 g/cm³.

Hence, the liquid in which iron can float is mercury.