Verified answer

Solid silver would sink in liquid silver. As objects go through the phase change from solid to liquid their molecules (or atoms in this case) move closer together and pack in tighter. Since there are more atoms per unit of area in a solid vs. a liquid then the solid is more dense...which means it will sink.

More platinum atoms are packed into a given volume (cm^3) than in the copper.

With water, the ice floats because of an unusual reaction where the crystals line up in such a way that the ice is less dense than the liquid water. In silver there is no real ifference when crystallation occurs other than release of energy. In the lquid the molecules are moving around faster and in the solid they are fixed in place. The cube would be neutral as far as floating or sinking.

The atoms packed into the platinum are more closely packed, as density is defined as how closely packed the atoms are.

although they are of the same element the solid silver will sink in hte liquid silver because solids are denser than liquid, ryt? how's that because solids are more tightly packed than liquids

for the 2nd quesn... the platinum is more tightly packed than copper since it contains more platinum per cc than the copper