Lead would float in mercury, as it is slightly less dense. (11.3 g/cc for lead, 13.5 g/cc for mercury)
In water mercury would sink very quickly as it is very heavy. Keep in mind that part of mercury dissolves in water and is extremely poisonous.
A diamond would sink in mercury because the density of a diamond (around 3.5 g/cm^3) is greater than that of mercury (around 13.5 g/cm^3), making the diamond denser than the liquid mercury.
If the low density water was put over another fluid of lower density it would sink but if it was put over a high density fluid like Mercury it would floats.
It would cause excessive mud and the swimming pool would sink slightly. It would only cause a sinkhole if there was a hole underground under the pool.
No, wood would not float in mercury. Mercury is a dense liquid metal, much denser than water, so wood would sink in it.
When you sink in the pool, it is because your body is denser than the water. This causes you to displace water and sink below the surface.
No, platinum will not sink in mercury because platinum is denser than mercury. Platinum has a density of 21.45 g/cm³, whereas mercury has a density of 13.53 g/cm³. Objects sink in fluids when their density is greater than that of the fluid, so platinum would actually float on the surface of mercury.
It is supposed to be inflated, because solid rings would sink the pool wall, and the water would escape.
Lead will sink in liquid mercury because lead is denser than mercury. Mercury is a heavy liquid metal, so most metals will sink when placed in it.
Oil is denser than cork, so the cork would float.
Mercury is a heavy metal, it will sink in sea water.