Most objects have their greatest density in which state/phase of matter?
Given the alternatives, solid, liquid, gas, most materials express their greatest density in the solid state. Obviously gases, with a great deal of empty space between particles are non-starters.
But there is one very important exception. Ice is less dense than its liquid state. Ice cubes placed in water float; ice bergs in the ocean also float (think Titanic), and of course the ice will be more buoyant in salt water.